<?xml version="1.0" encoding="US-ASCII"?>
<!--XBRL Document Created with WebFilings-->
<!-- -->
<linkbase xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" xmlns="http://www.xbrl.org/2003/linkbase" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <roleRef roleURI="http://www.fortinet.com/role/AccumulatedOtherComprehensiveIncome" xlink:href="ftnt-20140331.xsd#AccumulatedOtherComprehensiveIncome" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/AccumulatedOtherComprehensiveIncomeChangesInAccumulatedBalancesOfOtherComprehensiveIncomedetails" xlink:href="ftnt-20140331.xsd#AccumulatedOtherComprehensiveIncomeChangesInAccumulatedBalancesOfOtherComprehensiveIncomedetails" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/AccumulatedOtherComprehensiveIncomeReclassificationOutOfAccumulatedOtherComprehensiveIncomeDetails" xlink:href="ftnt-20140331.xsd#AccumulatedOtherComprehensiveIncomeReclassificationOutOfAccumulatedOtherComprehensiveIncomeDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/AccumulatedOtherComprehensiveIncomeTables" xlink:href="ftnt-20140331.xsd#AccumulatedOtherComprehensiveIncomeTables" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/BusinessCombinations" xlink:href="ftnt-20140331.xsd#BusinessCombinations" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/BusinessCombinations2013AcquisitionsDetails" xlink:href="ftnt-20140331.xsd#BusinessCombinations2013AcquisitionsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/BusinessCombinationsBusinessCombinationsTables" xlink:href="ftnt-20140331.xsd#BusinessCombinationsBusinessCombinationsTables" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/CommitmentsAndContingencies" xlink:href="ftnt-20140331.xsd#CommitmentsAndContingencies" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/CommitmentsAndContingenciesDetails" xlink:href="ftnt-20140331.xsd#CommitmentsAndContingenciesDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/CommitmentsAndContingenciesMinimumOperatingLeasePaymentsDetails" xlink:href="ftnt-20140331.xsd#CommitmentsAndContingenciesMinimumOperatingLeasePaymentsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/CommitmentsAndContingenciesTables" xlink:href="ftnt-20140331.xsd#CommitmentsAndContingenciesTables" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/CommitmentsAndContingenciesWarrantiesDetails" xlink:href="ftnt-20140331.xsd#CommitmentsAndContingenciesWarrantiesDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/ConsolidatedBalanceSheetsParenthetical" xlink:href="ftnt-20140331.xsd#ConsolidatedBalanceSheetsParenthetical" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/ConsolidatedBalanceSheetsUnaudited" xlink:href="ftnt-20140331.xsd#ConsolidatedBalanceSheetsUnaudited" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/ConsolidatedStatementsOfCashFlowsUnaudited" xlink:href="ftnt-20140331.xsd#ConsolidatedStatementsOfCashFlowsUnaudited" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/ConsolidatedStatementsOfComprehensiveIncomeUnaudited" xlink:href="ftnt-20140331.xsd#ConsolidatedStatementsOfComprehensiveIncomeUnaudited" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/ConsolidatedStatementsOfOperationsUnaudited" xlink:href="ftnt-20140331.xsd#ConsolidatedStatementsOfOperationsUnaudited" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/DeferredRevenue" xlink:href="ftnt-20140331.xsd#DeferredRevenue" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/DeferredRevenueDetails" xlink:href="ftnt-20140331.xsd#DeferredRevenueDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/DeferredRevenueTables" xlink:href="ftnt-20140331.xsd#DeferredRevenueTables" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/DocumentAndEntityInformation" xlink:href="ftnt-20140331.xsd#DocumentAndEntityInformation" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/EmployeeBenefitPlan" xlink:href="ftnt-20140331.xsd#EmployeeBenefitPlan" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/EmployeeBenefitPlanDetails" xlink:href="ftnt-20140331.xsd#EmployeeBenefitPlanDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/FinancialInstrumentsAndFairValue" xlink:href="ftnt-20140331.xsd#FinancialInstrumentsAndFairValue" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/FinancialInstrumentsAndFairValueChangeToContingentConsiderationLiabilityDetails" xlink:href="ftnt-20140331.xsd#FinancialInstrumentsAndFairValueChangeToContingentConsiderationLiabilityDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/FinancialInstrumentsAndFairValueFairValueMeasurementsDetails" xlink:href="ftnt-20140331.xsd#FinancialInstrumentsAndFairValueFairValueMeasurementsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/FinancialInstrumentsAndFairValueInvestmentsDetails" xlink:href="ftnt-20140331.xsd#FinancialInstrumentsAndFairValueInvestmentsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/FinancialInstrumentsAndFairValueTables" xlink:href="ftnt-20140331.xsd#FinancialInstrumentsAndFairValueTables" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/ForeignCurrencyDerivatives" xlink:href="ftnt-20140331.xsd#ForeignCurrencyDerivatives" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/ForeignCurrencyDerivativesDetails" xlink:href="ftnt-20140331.xsd#ForeignCurrencyDerivativesDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/ForeignCurrencyDerivativesTables" xlink:href="ftnt-20140331.xsd#ForeignCurrencyDerivativesTables" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/GoodwillAndOtherIntangibleAssetsnet" xlink:href="ftnt-20140331.xsd#GoodwillAndOtherIntangibleAssetsnet" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/GoodwillAndOtherIntangibleAssetsnetFiniteLivedIntangibleAssetsDetails" xlink:href="ftnt-20140331.xsd#GoodwillAndOtherIntangibleAssetsnetFiniteLivedIntangibleAssetsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/GoodwillAndOtherIntangibleAssetsnetGoodwillDetails" xlink:href="ftnt-20140331.xsd#GoodwillAndOtherIntangibleAssetsnetGoodwillDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/GoodwillAndOtherIntangibleAssetsnetTables" xlink:href="ftnt-20140331.xsd#GoodwillAndOtherIntangibleAssetsnetTables" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/IncomeTaxes" xlink:href="ftnt-20140331.xsd#IncomeTaxes" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/IncomeTaxesDetails" xlink:href="ftnt-20140331.xsd#IncomeTaxesDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/Inventory" xlink:href="ftnt-20140331.xsd#Inventory" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/InventoryDetails" xlink:href="ftnt-20140331.xsd#InventoryDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/InventoryTables" xlink:href="ftnt-20140331.xsd#InventoryTables" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/NetIncomePerShare" xlink:href="ftnt-20140331.xsd#NetIncomePerShare" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/NetIncomePerShareAntiDilutiveSecuritiesDetails" xlink:href="ftnt-20140331.xsd#NetIncomePerShareAntiDilutiveSecuritiesDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/NetIncomePerShareCalculationOfBasicAndDilutedDetails" xlink:href="ftnt-20140331.xsd#NetIncomePerShareCalculationOfBasicAndDilutedDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/NetIncomePerShareTables" xlink:href="ftnt-20140331.xsd#NetIncomePerShareTables" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/PropertyAndEquipmentnet" xlink:href="ftnt-20140331.xsd#PropertyAndEquipmentnet" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/PropertyAndEquipmentnetDetails" xlink:href="ftnt-20140331.xsd#PropertyAndEquipmentnetDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/PropertyAndEquipmentnetTables" xlink:href="ftnt-20140331.xsd#PropertyAndEquipmentnetTables" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/SegmentInformation" xlink:href="ftnt-20140331.xsd#SegmentInformation" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/SegmentInformationDetails" xlink:href="ftnt-20140331.xsd#SegmentInformationDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/SegmentInformationTables" xlink:href="ftnt-20140331.xsd#SegmentInformationTables" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/StockholdersEquity" xlink:href="ftnt-20140331.xsd#StockholdersEquity" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/StockholdersEquityAllocationOfStockBasedCompensationExpenseDetails" xlink:href="ftnt-20140331.xsd#StockholdersEquityAllocationOfStockBasedCompensationExpenseDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/StockholdersEquityDetails" xlink:href="ftnt-20140331.xsd#StockholdersEquityDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/StockholdersEquityEsppInformationDetails" xlink:href="ftnt-20140331.xsd#StockholdersEquityEsppInformationDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/StockholdersEquityRestrictedStockUnitsActivityDetails" xlink:href="ftnt-20140331.xsd#StockholdersEquityRestrictedStockUnitsActivityDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/StockholdersEquityShareRepurchaseProgramDetails" xlink:href="ftnt-20140331.xsd#StockholdersEquityShareRepurchaseProgramDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/StockholdersEquityTables" xlink:href="ftnt-20140331.xsd#StockholdersEquityTables" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/SummaryOfSignificantAccountingPolicies" xlink:href="ftnt-20140331.xsd#SummaryOfSignificantAccountingPolicies" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/SummaryOfSignificantAccountingPoliciesPolicies" xlink:href="ftnt-20140331.xsd#SummaryOfSignificantAccountingPoliciesPolicies" xlink:type="simple" />
  <roleRef roleURI="http://www.fortinet.com/role/SummaryOfSignificantAccountingPoliciesPropertyAndEquipmentDetails" xlink:href="ftnt-20140331.xsd#SummaryOfSignificantAccountingPoliciesPropertyAndEquipmentDetails" xlink:type="simple" />
  <arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all" xlink:type="simple" />
  <arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default" xlink:type="simple" />
  <arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain" xlink:type="simple" />
  <arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member" xlink:type="simple" />
  <arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension" xlink:type="simple" />
  <definitionLink xlink:role="http://www.fortinet.com/role/AccumulatedOtherComprehensiveIncome" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/AccumulatedOtherComprehensiveIncomeChangesInAccumulatedBalancesOfOtherComprehensiveIncomedetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_7A25C35C863A73DF9769AFA8BA5DF559" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossTable" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_065DC939E6EEE2F4D5B6AFA8BA5C0D61" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_7A25C35C863A73DF9769AFA8BA5DF559" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_065DC939E6EEE2F4D5B6AFA8BA5C0D61" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_6007DD8E25ADFC6526D0AFA8BA5CDC9E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_065DC939E6EEE2F4D5B6AFA8BA5C0D61" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_6007DD8E25ADFC6526D0AFA8BA5CDC9E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_46CD6C641B464BEBA14FAFA8BA5D1145_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_6007DD8E25ADFC6526D0AFA8BA5CDC9E" xlink:to="loc_us-gaap_EquityComponentDomain_46CD6C641B464BEBA14FAFA8BA5D1145_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_46CD6C641B464BEBA14FAFA8BA5D1145" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_6007DD8E25ADFC6526D0AFA8BA5CDC9E" xlink:to="loc_us-gaap_EquityComponentDomain_46CD6C641B464BEBA14FAFA8BA5D1145" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccumulatedTranslationAdjustmentMember" xlink:label="loc_us-gaap_AccumulatedTranslationAdjustmentMember_2DE537AE0E4266963057AFA8BA5D789F" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_46CD6C641B464BEBA14FAFA8BA5D1145" xlink:to="loc_us-gaap_AccumulatedTranslationAdjustmentMember_2DE537AE0E4266963057AFA8BA5D789F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember" xlink:label="loc_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember_90CA2E299A48BB202665AFA8BA5DC527" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_46CD6C641B464BEBA14FAFA8BA5D1145" xlink:to="loc_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember_90CA2E299A48BB202665AFA8BA5DC527" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_AccumulatedOtherComprehensiveIncomeRollForward" xlink:label="loc_ftnt_AccumulatedOtherComprehensiveIncomeRollForward_CC52BF534DA88BD15496AFA8BA5D6959" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_7A25C35C863A73DF9769AFA8BA5DF559" xlink:to="loc_ftnt_AccumulatedOtherComprehensiveIncomeRollForward_CC52BF534DA88BD15496AFA8BA5D6959" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1_87D194B689BE3CD11EE1AFA8BA622D3F" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ftnt_AccumulatedOtherComprehensiveIncomeRollForward_CC52BF534DA88BD15496AFA8BA5D6959" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1_87D194B689BE3CD11EE1AFA8BA622D3F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsBeforeTax" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsBeforeTax_A487DD9029F98E7B1103AFA8BA62D7C3" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ftnt_AccumulatedOtherComprehensiveIncomeRollForward_CC52BF534DA88BD15496AFA8BA5D6959" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsBeforeTax_A487DD9029F98E7B1103AFA8BA62D7C3" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax" xlink:label="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax_76D3A4B7BF954ECEC920AFA8BA62D5AF" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ftnt_AccumulatedOtherComprehensiveIncomeRollForward_CC52BF534DA88BD15496AFA8BA5D6959" xlink:to="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax_76D3A4B7BF954ECEC920AFA8BA62D5AF" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeTax" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeTax_C23CAA5AD8F3E64E81B0AFA8BA622068" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ftnt_AccumulatedOtherComprehensiveIncomeRollForward_CC52BF534DA88BD15496AFA8BA5D6959" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeTax_C23CAA5AD8F3E64E81B0AFA8BA622068" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_AccumulatedOtherComprehensiveIncomeTaxRollForward" xlink:label="loc_ftnt_AccumulatedOtherComprehensiveIncomeTaxRollForward_3EB43E896F6BF26D1CAAAFA8BA63790E" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_7A25C35C863A73DF9769AFA8BA5DF559" xlink:to="loc_ftnt_AccumulatedOtherComprehensiveIncomeTaxRollForward_3EB43E896F6BF26D1CAAAFA8BA63790E" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_AccumulatedOtherComprehensiveIncomeLossTax" xlink:label="loc_ftnt_AccumulatedOtherComprehensiveIncomeLossTax_21669EE0756A46BD2DFDAFA8BA634986" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ftnt_AccumulatedOtherComprehensiveIncomeTaxRollForward_3EB43E896F6BF26D1CAAAFA8BA63790E" xlink:to="loc_ftnt_AccumulatedOtherComprehensiveIncomeLossTax_21669EE0756A46BD2DFDAFA8BA634986" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_OtherComprehensiveIncomeLossbeforeReclassificationsTax" xlink:label="loc_ftnt_OtherComprehensiveIncomeLossbeforeReclassificationsTax_303ACC9ACBD0B147101DAFA8BA63634B" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ftnt_AccumulatedOtherComprehensiveIncomeTaxRollForward_3EB43E896F6BF26D1CAAAFA8BA63790E" xlink:to="loc_ftnt_OtherComprehensiveIncomeLossbeforeReclassificationsTax_303ACC9ACBD0B147101DAFA8BA63634B" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_ReclassificationfromAccumulatedOtherComprehensiveIncomeCurrentPeriodTax" xlink:label="loc_ftnt_ReclassificationfromAccumulatedOtherComprehensiveIncomeCurrentPeriodTax_907279C327CF2E146D2CAFA8BA63F856" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ftnt_AccumulatedOtherComprehensiveIncomeTaxRollForward_3EB43E896F6BF26D1CAAAFA8BA63790E" xlink:to="loc_ftnt_ReclassificationfromAccumulatedOtherComprehensiveIncomeCurrentPeriodTax_907279C327CF2E146D2CAFA8BA63F856" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossTax" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossTax_F49B54233EFE644F5838AFA8BA632299" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ftnt_AccumulatedOtherComprehensiveIncomeTaxRollForward_3EB43E896F6BF26D1CAAAFA8BA63790E" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossTax_F49B54233EFE644F5838AFA8BA632299" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fortinet.com/role/AccumulatedOtherComprehensiveIncomeReclassificationOutOfAccumulatedOtherComprehensiveIncomeDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems" xlink:label="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_B9410257461A6D698584D38FD6B3A491" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_6783FE0D780515CBB387D38FD6B34DCC" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_B9410257461A6D698584D38FD6B3A491" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_6783FE0D780515CBB387D38FD6B34DCC" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_B2503B012C40185AE969D38FD6B37B63" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_6783FE0D780515CBB387D38FD6B34DCC" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_B2503B012C40185AE969D38FD6B37B63" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_C5ABB519848130DA1582D38FD6B3CCFF_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_B2503B012C40185AE969D38FD6B37B63" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_C5ABB519848130DA1582D38FD6B3CCFF_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_C5ABB519848130DA1582D38FD6B3CCFF" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_B2503B012C40185AE969D38FD6B37B63" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_C5ABB519848130DA1582D38FD6B3CCFF" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember_56629E46FA68BCFF655DD38FD6B346C0" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_C5ABB519848130DA1582D38FD6B3CCFF" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember_56629E46FA68BCFF655DD38FD6B346C0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherNonoperatingIncomeExpense" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_D4EED46E353C7EA1E10CD38FD6B3146D" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_B9410257461A6D698584D38FD6B3A491" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_D4EED46E353C7EA1E10CD38FD6B3146D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_24C6F76AAF5AA0591360D38FD6B38CBB" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_B9410257461A6D698584D38FD6B3A491" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_24C6F76AAF5AA0591360D38FD6B38CBB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="loc_us-gaap_NetIncomeLoss_E155E26333AF76DAA9FED38FD6B4F0AA" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_B9410257461A6D698584D38FD6B3A491" xlink:to="loc_us-gaap_NetIncomeLoss_E155E26333AF76DAA9FED38FD6B4F0AA" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fortinet.com/role/AccumulatedOtherComprehensiveIncomeTables" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/BusinessCombinations" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/BusinessCombinations2013AcquisitionsDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_D7023C1E0B00D5F4E6C2D385A119EAEE" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_7A22F11C71C49E28098FD385A1178356" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D7023C1E0B00D5F4E6C2D385A119EAEE" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_7A22F11C71C49E28098FD385A1178356" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_D25D96E0D467CAAD503ED385A117A21F" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_7A22F11C71C49E28098FD385A1178356" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_D25D96E0D467CAAD503ED385A117A21F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_99AB44986B8BA1A115FED385A11717BB_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_D25D96E0D467CAAD503ED385A117A21F" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_99AB44986B8BA1A115FED385A11717BB_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_99AB44986B8BA1A115FED385A11717BB" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_D25D96E0D467CAAD503ED385A117A21F" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_99AB44986B8BA1A115FED385A11717BB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InProcessResearchAndDevelopmentMember" xlink:label="loc_us-gaap_InProcessResearchAndDevelopmentMember_A72E8D1F74DF5A46A4C9D385A117CBB0" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_99AB44986B8BA1A115FED385A11717BB" xlink:to="loc_us-gaap_InProcessResearchAndDevelopmentMember_A72E8D1F74DF5A46A4C9D385A117CBB0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_79C48E7925186ECA196DD385A118B30B" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_7A22F11C71C49E28098FD385A1178356" xlink:to="loc_us-gaap_RangeAxis_79C48E7925186ECA196DD385A118B30B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_F15618B4B1262B96AE67D385A1180E09_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_79C48E7925186ECA196DD385A118B30B" xlink:to="loc_us-gaap_RangeMember_F15618B4B1262B96AE67D385A1180E09_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_F15618B4B1262B96AE67D385A1180E09" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_79C48E7925186ECA196DD385A118B30B" xlink:to="loc_us-gaap_RangeMember_F15618B4B1262B96AE67D385A1180E09" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_PayableafterEighteenMonthsfromAcquisitionDateMember" xlink:label="loc_ftnt_PayableafterEighteenMonthsfromAcquisitionDateMember_3CF674E06F5CD1833DE4D385A11867A3" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_F15618B4B1262B96AE67D385A1180E09" xlink:to="loc_ftnt_PayableafterEighteenMonthsfromAcquisitionDateMember_3CF674E06F5CD1833DE4D385A11867A3" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_PayableafterTwoYearsfromAcquisitionDateMember" xlink:label="loc_ftnt_PayableafterTwoYearsfromAcquisitionDateMember_61B0443186BC85B06C84D385A118698C" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_F15618B4B1262B96AE67D385A1180E09" xlink:to="loc_ftnt_PayableafterTwoYearsfromAcquisitionDateMember_61B0443186BC85B06C84D385A118698C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_A0B2ABADE2676151EC41D385A1185FA2" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_7A22F11C71C49E28098FD385A1178356" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_A0B2ABADE2676151EC41D385A1185FA2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_C735B58EFD869A20D78FD385A1186260_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_A0B2ABADE2676151EC41D385A1185FA2" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_C735B58EFD869A20D78FD385A1186260_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_C735B58EFD869A20D78FD385A1186260" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_A0B2ABADE2676151EC41D385A1185FA2" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_C735B58EFD869A20D78FD385A1186260" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DevelopedTechnologyRightsMember" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_AC70BA498DF3244C1ECCD385A118477C" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_C735B58EFD869A20D78FD385A1186260" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_AC70BA498DF3244C1ECCD385A118477C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CustomerRelationshipsMember" xlink:label="loc_us-gaap_CustomerRelationshipsMember_54E4563958BF13629190D385A1187475" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_C735B58EFD869A20D78FD385A1186260" xlink:to="loc_us-gaap_CustomerRelationshipsMember_54E4563958BF13629190D385A1187475" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_0023A83BF9A383744C08D385A118DC8B" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_7A22F11C71C49E28098FD385A1178356" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_0023A83BF9A383744C08D385A118DC8B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_EC1E62C71EB82F98E920D385A11875C4_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_0023A83BF9A383744C08D385A118DC8B" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_EC1E62C71EB82F98E920D385A11875C4_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_EC1E62C71EB82F98E920D385A11875C4" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_0023A83BF9A383744C08D385A118DC8B" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_EC1E62C71EB82F98E920D385A11875C4" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_CoyotePointSystemsInc.Member" xlink:label="loc_ftnt_CoyotePointSystemsInc.Member_88B3F0E022974FD75859D385A1182E06" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_EC1E62C71EB82F98E920D385A11875C4" xlink:to="loc_ftnt_CoyotePointSystemsInc.Member_88B3F0E022974FD75859D385A1182E06" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PaymentsToAcquireBusinessesGross" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesGross_7E6AF82F1B21A8C3FF19D385A119EDF5" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D7023C1E0B00D5F4E6C2D385A119EAEE" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesGross_7E6AF82F1B21A8C3FF19D385A119EDF5" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh_529AD7035404E02E91C6D385A1198FD9" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D7023C1E0B00D5F4E6C2D385A119EAEE" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh_529AD7035404E02E91C6D385A1198FD9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents_B3C0708CE9897E7096F7D385A1197406" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D7023C1E0B00D5F4E6C2D385A119EAEE" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents_B3C0708CE9897E7096F7D385A1197406" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsOther" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsOther_B5724C04348880F928EBD385A119B67D" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D7023C1E0B00D5F4E6C2D385A119EAEE" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsOther_B5724C04348880F928EBD385A119B67D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_A05FE4FFDEDF15518C38D385A1197925" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D7023C1E0B00D5F4E6C2D385A119EAEE" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_A05FE4FFDEDF15518C38D385A1197925" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets_D866157C8408168F7AE1D385A1190DE2" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D7023C1E0B00D5F4E6C2D385A119EAEE" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets_D866157C8408168F7AE1D385A1190DE2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_Goodwill" xlink:label="loc_us-gaap_Goodwill_2DD082E08900717C7F86D385A1194B02" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D7023C1E0B00D5F4E6C2D385A119EAEE" xlink:to="loc_us-gaap_Goodwill_2DD082E08900717C7F86D385A1194B02" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets_263CADAF02BF2FE943C4D385A1197E0B" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D7023C1E0B00D5F4E6C2D385A119EAEE" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets_263CADAF02BF2FE943C4D385A1197E0B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets_4973F1621E603F91355DD385A1192FC0" xlink:type="locator" />
    <definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D7023C1E0B00D5F4E6C2D385A119EAEE" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets_4973F1621E603F91355DD385A1192FC0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilities" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilities_FCB1C0DF51C25F26A694D385A11931B5" xlink:type="locator" />
    <definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D7023C1E0B00D5F4E6C2D385A119EAEE" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilities_FCB1C0DF51C25F26A694D385A11931B5" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilities" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilities_F8DDFE04722BA7827532D385A11946AC" xlink:type="locator" />
    <definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D7023C1E0B00D5F4E6C2D385A119EAEE" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilities_F8DDFE04722BA7827532D385A11946AC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities_EBC8866E7E7EAF844076D385A11914B1" xlink:type="locator" />
    <definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D7023C1E0B00D5F4E6C2D385A119EAEE" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities_EBC8866E7E7EAF844076D385A11914B1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet_8E50148FE35A032DD4B2D385A11A8FAD" xlink:type="locator" />
    <definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D7023C1E0B00D5F4E6C2D385A119EAEE" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet_8E50148FE35A032DD4B2D385A11A8FAD" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_8AC1F5E70A8FC96B8924D385A11A9342" xlink:type="locator" />
    <definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D7023C1E0B00D5F4E6C2D385A119EAEE" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_8AC1F5E70A8FC96B8924D385A11A9342" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fortinet.com/role/BusinessCombinationsBusinessCombinationsTables" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/CommitmentsAndContingencies" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/CommitmentsAndContingenciesDetails" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/CommitmentsAndContingenciesMinimumOperatingLeasePaymentsDetails" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/CommitmentsAndContingenciesTables" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/CommitmentsAndContingenciesWarrantiesDetails" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/ConsolidatedBalanceSheetsParenthetical" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_26F5ABD6C7593655C024D306D154D8FB" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_8F1BC9DBE6C995E05C13D306D15463F7" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_26F5ABD6C7593655C024D306D154D8FB" xlink:to="loc_us-gaap_StatementTable_8F1BC9DBE6C995E05C13D306D15463F7" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementScenarioAxis" xlink:label="loc_us-gaap_StatementScenarioAxis_E82FE26E0AC97294295ED306D15414E2" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_8F1BC9DBE6C995E05C13D306D15463F7" xlink:to="loc_us-gaap_StatementScenarioAxis_E82FE26E0AC97294295ED306D15414E2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScenarioUnspecifiedDomain" xlink:label="loc_us-gaap_ScenarioUnspecifiedDomain_BA37B0CEEC9FFD346B19D306D15478CE_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementScenarioAxis_E82FE26E0AC97294295ED306D15414E2" xlink:to="loc_us-gaap_ScenarioUnspecifiedDomain_BA37B0CEEC9FFD346B19D306D15478CE_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScenarioUnspecifiedDomain" xlink:label="loc_us-gaap_ScenarioUnspecifiedDomain_BA37B0CEEC9FFD346B19D306D15478CE" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementScenarioAxis_E82FE26E0AC97294295ED306D15414E2" xlink:to="loc_us-gaap_ScenarioUnspecifiedDomain_BA37B0CEEC9FFD346B19D306D15478CE" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_AllowanceForDoubtfulAccountsReceivableandSalesReturns" xlink:label="loc_ftnt_AllowanceForDoubtfulAccountsReceivableandSalesReturns_08ABF9729D8BFD359920D306D154EF33" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_26F5ABD6C7593655C024D306D154D8FB" xlink:to="loc_ftnt_AllowanceForDoubtfulAccountsReceivableandSalesReturns_08ABF9729D8BFD359920D306D154EF33" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_BC5392682D555C41B3ACD306D154F1E1" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_26F5ABD6C7593655C024D306D154D8FB" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_BC5392682D555C41B3ACD306D154F1E1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommonStockSharesAuthorized" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_A9D4123515F6109BA55FD306D154B399" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_26F5ABD6C7593655C024D306D154D8FB" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_A9D4123515F6109BA55FD306D154B399" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommonStockSharesIssued" xlink:label="loc_us-gaap_CommonStockSharesIssued_ADBAD3E30FFB5F4DD004D306D1542362" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_26F5ABD6C7593655C024D306D154D8FB" xlink:to="loc_us-gaap_CommonStockSharesIssued_ADBAD3E30FFB5F4DD004D306D1542362" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommonStockSharesOutstanding" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_9EFEA9B9B855BDDE3CE0D306D1542EAD" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_26F5ABD6C7593655C024D306D154D8FB" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_9EFEA9B9B855BDDE3CE0D306D1542EAD" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fortinet.com/role/ConsolidatedBalanceSheetsUnaudited" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_35DE36879216D63C073CD31C48AD873F" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_C624764409C6665DFF3FD31C48AD3122" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_35DE36879216D63C073CD31C48AD873F" xlink:to="loc_us-gaap_StatementTable_C624764409C6665DFF3FD31C48AD3122" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementScenarioAxis" xlink:label="loc_us-gaap_StatementScenarioAxis_AE0B10F86FDC9A625071D31C48AD587F" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_C624764409C6665DFF3FD31C48AD3122" xlink:to="loc_us-gaap_StatementScenarioAxis_AE0B10F86FDC9A625071D31C48AD587F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScenarioUnspecifiedDomain" xlink:label="loc_us-gaap_ScenarioUnspecifiedDomain_7793F43EFC67F3A0BCE7D31C48ADFAA1_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementScenarioAxis_AE0B10F86FDC9A625071D31C48AD587F" xlink:to="loc_us-gaap_ScenarioUnspecifiedDomain_7793F43EFC67F3A0BCE7D31C48ADFAA1_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScenarioUnspecifiedDomain" xlink:label="loc_us-gaap_ScenarioUnspecifiedDomain_7793F43EFC67F3A0BCE7D31C48ADFAA1" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementScenarioAxis_AE0B10F86FDC9A625071D31C48AD587F" xlink:to="loc_us-gaap_ScenarioUnspecifiedDomain_7793F43EFC67F3A0BCE7D31C48ADFAA1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AssetsAbstract" xlink:label="loc_us-gaap_AssetsAbstract_A08E4EDEF0F747F69D60D31C48AE5C6E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_35DE36879216D63C073CD31C48AD873F" xlink:to="loc_us-gaap_AssetsAbstract_A08E4EDEF0F747F69D60D31C48AE5C6E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AssetsCurrentAbstract" xlink:label="loc_us-gaap_AssetsCurrentAbstract_9FC8C596A23686C0C57DD31C48AE7595" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_A08E4EDEF0F747F69D60D31C48AE5C6E" xlink:to="loc_us-gaap_AssetsCurrentAbstract_9FC8C596A23686C0C57DD31C48AE7595" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_7F27A8041D0EEDD23803D31C48AEF13A" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_9FC8C596A23686C0C57DD31C48AE7595" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_7F27A8041D0EEDD23803D31C48AEF13A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShortTermInvestments" xlink:label="loc_us-gaap_ShortTermInvestments_A524F2EF1792DB60988FD31C48AEC191" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_9FC8C596A23686C0C57DD31C48AE7595" xlink:to="loc_us-gaap_ShortTermInvestments_A524F2EF1792DB60988FD31C48AEC191" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccountsReceivableNetCurrent" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_2B0BF784F1E1FFDB5824D31C48AEF31C" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_9FC8C596A23686C0C57DD31C48AE7595" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_2B0BF784F1E1FFDB5824D31C48AEF31C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InventoryNet" xlink:label="loc_us-gaap_InventoryNet_C25BAF223D5450BB9AF4D31C48AF8D87" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_9FC8C596A23686C0C57DD31C48AE7595" xlink:to="loc_us-gaap_InventoryNet_C25BAF223D5450BB9AF4D31C48AF8D87" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredTaxAssetsNetCurrent" xlink:label="loc_us-gaap_DeferredTaxAssetsNetCurrent_0A7B0F28D43A7EA52E33D31C48AF87B0" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_9FC8C596A23686C0C57DD31C48AE7595" xlink:to="loc_us-gaap_DeferredTaxAssetsNetCurrent_0A7B0F28D43A7EA52E33D31C48AF87B0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_DE1B8D09D7A6430933D3D31C48AF922A" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_9FC8C596A23686C0C57DD31C48AE7595" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_DE1B8D09D7A6430933D3D31C48AF922A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AssetsCurrent" xlink:label="loc_us-gaap_AssetsCurrent_BA82D9E32A6EF5D66CA3D31C48AF314B" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_9FC8C596A23686C0C57DD31C48AE7595" xlink:to="loc_us-gaap_AssetsCurrent_BA82D9E32A6EF5D66CA3D31C48AF314B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_7F0A1413EBE9C63EB67DD31C48AFCA1D" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_A08E4EDEF0F747F69D60D31C48AE5C6E" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_7F0A1413EBE9C63EB67DD31C48AFCA1D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredTaxAssetsNetNoncurrent" xlink:label="loc_us-gaap_DeferredTaxAssetsNetNoncurrent_7247D4293EA3443EE97AD31C48AFCEE5" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_A08E4EDEF0F747F69D60D31C48AE5C6E" xlink:to="loc_us-gaap_DeferredTaxAssetsNetNoncurrent_7247D4293EA3443EE97AD31C48AFCEE5" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermInvestments" xlink:label="loc_us-gaap_LongTermInvestments_CB720B477570FE554D5ED31C48AF76DD" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_A08E4EDEF0F747F69D60D31C48AE5C6E" xlink:to="loc_us-gaap_LongTermInvestments_CB720B477570FE554D5ED31C48AF76DD" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_Goodwill" xlink:label="loc_us-gaap_Goodwill_A0F7351432B5E50B398CD31C48AF53A1" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_A08E4EDEF0F747F69D60D31C48AE5C6E" xlink:to="loc_us-gaap_Goodwill_A0F7351432B5E50B398CD31C48AF53A1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_B77D1C8FCA5241329F3AD31C48AF87EE" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_A08E4EDEF0F747F69D60D31C48AE5C6E" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_B77D1C8FCA5241329F3AD31C48AF87EE" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherAssetsNoncurrent" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_1D612DCD6B2618699977D31C48AF1014" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_A08E4EDEF0F747F69D60D31C48AE5C6E" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_1D612DCD6B2618699977D31C48AF1014" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_Assets" xlink:label="loc_us-gaap_Assets_EFDD5F74E4EAE94C6E88D31C48AF5D9C" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_A08E4EDEF0F747F69D60D31C48AE5C6E" xlink:to="loc_us-gaap_Assets_EFDD5F74E4EAE94C6E88D31C48AF5D9C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_5267D3987BF6B8B69F0FD31C48AF1B67" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_35DE36879216D63C073CD31C48AD873F" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_5267D3987BF6B8B69F0FD31C48AF1B67" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilitiesCurrentAbstract" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_F3B3A73A83C20F3B09FDD31C48B02E3B" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_5267D3987BF6B8B69F0FD31C48AF1B67" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_F3B3A73A83C20F3B09FDD31C48B02E3B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccountsPayableCurrent" xlink:label="loc_us-gaap_AccountsPayableCurrent_28C30243711F7CF63801D31C48B03D9A" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_F3B3A73A83C20F3B09FDD31C48B02E3B" xlink:to="loc_us-gaap_AccountsPayableCurrent_28C30243711F7CF63801D31C48B03D9A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccruedLiabilitiesCurrent" xlink:label="loc_us-gaap_AccruedLiabilitiesCurrent_3FDA950DCCD259BE9A36D31C48B02B91" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_F3B3A73A83C20F3B09FDD31C48B02E3B" xlink:to="loc_us-gaap_AccruedLiabilitiesCurrent_3FDA950DCCD259BE9A36D31C48B02B91" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EmployeeRelatedLiabilitiesCurrent" xlink:label="loc_us-gaap_EmployeeRelatedLiabilitiesCurrent_9CFF41B5E52526F19FDED31C48B08A03" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_F3B3A73A83C20F3B09FDD31C48B02E3B" xlink:to="loc_us-gaap_EmployeeRelatedLiabilitiesCurrent_9CFF41B5E52526F19FDED31C48B08A03" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccruedIncomeTaxesCurrent" xlink:label="loc_us-gaap_AccruedIncomeTaxesCurrent_8388DB5C508EBCCC4109D31C48B046BD" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_F3B3A73A83C20F3B09FDD31C48B02E3B" xlink:to="loc_us-gaap_AccruedIncomeTaxesCurrent_8388DB5C508EBCCC4109D31C48B046BD" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredRevenueCurrent" xlink:label="loc_us-gaap_DeferredRevenueCurrent_EED2B6DBFFDA4F97F157D31C48B080E7" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_F3B3A73A83C20F3B09FDD31C48B02E3B" xlink:to="loc_us-gaap_DeferredRevenueCurrent_EED2B6DBFFDA4F97F157D31C48B080E7" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilitiesCurrent" xlink:label="loc_us-gaap_LiabilitiesCurrent_0EB13F2BE6EA0D667415D31C48B0FC59" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_F3B3A73A83C20F3B09FDD31C48B02E3B" xlink:to="loc_us-gaap_LiabilitiesCurrent_0EB13F2BE6EA0D667415D31C48B0FC59" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredRevenueNoncurrent" xlink:label="loc_us-gaap_DeferredRevenueNoncurrent_ABCE9A6DDEAEC7C7A769D31C48B07D66" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_5267D3987BF6B8B69F0FD31C48AF1B67" xlink:to="loc_us-gaap_DeferredRevenueNoncurrent_ABCE9A6DDEAEC7C7A769D31C48B07D66" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccruedIncomeTaxesNoncurrent" xlink:label="loc_us-gaap_AccruedIncomeTaxesNoncurrent_4DB70A31C392E6CF9E97D31C48B0A207" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_5267D3987BF6B8B69F0FD31C48AF1B67" xlink:to="loc_us-gaap_AccruedIncomeTaxesNoncurrent_4DB70A31C392E6CF9E97D31C48B0A207" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherLiabilitiesNoncurrent" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_65E68CA9D26FB031284ED31C48B0B657" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_5267D3987BF6B8B69F0FD31C48AF1B67" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_65E68CA9D26FB031284ED31C48B0B657" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_Liabilities" xlink:label="loc_us-gaap_Liabilities_5E2FAAD591EFA24BCDF8D31C48B0814C" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_5267D3987BF6B8B69F0FD31C48AF1B67" xlink:to="loc_us-gaap_Liabilities_5E2FAAD591EFA24BCDF8D31C48B0814C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommitmentsAndContingencies" xlink:label="loc_us-gaap_CommitmentsAndContingencies_0779F4612849CE1C7EF8D31C48B059BB" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_5267D3987BF6B8B69F0FD31C48AF1B67" xlink:to="loc_us-gaap_CommitmentsAndContingencies_0779F4612849CE1C7EF8D31C48B059BB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockholdersEquityAbstract" xlink:label="loc_us-gaap_StockholdersEquityAbstract_B89ED372319FC3CBBEFED31C48B089D9" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_5267D3987BF6B8B69F0FD31C48AF1B67" xlink:to="loc_us-gaap_StockholdersEquityAbstract_B89ED372319FC3CBBEFED31C48B089D9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommonStockValue" xlink:label="loc_us-gaap_CommonStockValue_F7ED85F8C30EFA1C3492D31C48B0F383" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_B89ED372319FC3CBBEFED31C48B089D9" xlink:to="loc_us-gaap_CommonStockValue_F7ED85F8C30EFA1C3492D31C48B0F383" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AdditionalPaidInCapitalCommonStock" xlink:label="loc_us-gaap_AdditionalPaidInCapitalCommonStock_A5A9373840269089E94CD31C48B0BF97" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_B89ED372319FC3CBBEFED31C48B089D9" xlink:to="loc_us-gaap_AdditionalPaidInCapitalCommonStock_A5A9373840269089E94CD31C48B0BF97" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_608E0BD89EFB77E71939D31C48B0D191" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_B89ED372319FC3CBBEFED31C48B089D9" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_608E0BD89EFB77E71939D31C48B0D191" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RetainedEarningsAccumulatedDeficit" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_A0E9D2EC7AC8007B1F75D31C48B10987" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_B89ED372319FC3CBBEFED31C48B089D9" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_A0E9D2EC7AC8007B1F75D31C48B10987" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockholdersEquity" xlink:label="loc_us-gaap_StockholdersEquity_7412387328FAEF31A696D31C48B10DE4" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_B89ED372319FC3CBBEFED31C48B089D9" xlink:to="loc_us-gaap_StockholdersEquity_7412387328FAEF31A696D31C48B10DE4" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquity" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_9E66BD5C140F4CC5A6E2D31C48B17EE3" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_5267D3987BF6B8B69F0FD31C48AF1B67" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_9E66BD5C140F4CC5A6E2D31C48B17EE3" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fortinet.com/role/ConsolidatedStatementsOfCashFlowsUnaudited" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_FF5A4F619075C45A2242D31C7012FF9A" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_0A228D3DA9FF7E358058D31C7012E49B" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_FF5A4F619075C45A2242D31C7012FF9A" xlink:to="loc_us-gaap_StatementTable_0A228D3DA9FF7E358058D31C7012E49B" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementScenarioAxis" xlink:label="loc_us-gaap_StatementScenarioAxis_EFEC908219D2F2A280ADD31C70129EB5" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_0A228D3DA9FF7E358058D31C7012E49B" xlink:to="loc_us-gaap_StatementScenarioAxis_EFEC908219D2F2A280ADD31C70129EB5" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScenarioUnspecifiedDomain" xlink:label="loc_us-gaap_ScenarioUnspecifiedDomain_DC0D351F8564222F7171D31C7012EA9E_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementScenarioAxis_EFEC908219D2F2A280ADD31C70129EB5" xlink:to="loc_us-gaap_ScenarioUnspecifiedDomain_DC0D351F8564222F7171D31C7012EA9E_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScenarioUnspecifiedDomain" xlink:label="loc_us-gaap_ScenarioUnspecifiedDomain_DC0D351F8564222F7171D31C7012EA9E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementScenarioAxis_EFEC908219D2F2A280ADD31C70129EB5" xlink:to="loc_us-gaap_ScenarioUnspecifiedDomain_DC0D351F8564222F7171D31C7012EA9E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_9B05992D9BD2E6889C67D31C701216F2" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_FF5A4F619075C45A2242D31C7012FF9A" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_9B05992D9BD2E6889C67D31C701216F2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="loc_us-gaap_NetIncomeLoss_2694E64ECC69EEA91B8CD31C70120C67" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_9B05992D9BD2E6889C67D31C701216F2" xlink:to="loc_us-gaap_NetIncomeLoss_2694E64ECC69EEA91B8CD31C70120C67" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_42B288DA57673EE5B9A0D31C70121A07" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_9B05992D9BD2E6889C67D31C701216F2" xlink:to="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_42B288DA57673EE5B9A0D31C70121A07" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DepreciationDepletionAndAmortization" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_CF16B8D7BB0C157760BFD31C70132DC4" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_42B288DA57673EE5B9A0D31C70121A07" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_CF16B8D7BB0C157760BFD31C70132DC4" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments" xlink:label="loc_us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments_A968996BDCD6033A02CED31C7013CC4E" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_42B288DA57673EE5B9A0D31C70121A07" xlink:to="loc_us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments_A968996BDCD6033A02CED31C7013CC4E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensation" xlink:label="loc_us-gaap_ShareBasedCompensation_1DDDFD6465A35ACB0067D31C70130B7F" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_42B288DA57673EE5B9A0D31C70121A07" xlink:to="loc_us-gaap_ShareBasedCompensation_1DDDFD6465A35ACB0067D31C70130B7F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ExcessTaxBenefitFromShareBasedCompensationOperatingActivities" xlink:label="loc_us-gaap_ExcessTaxBenefitFromShareBasedCompensationOperatingActivities_7B28E5BAF69BCC7149C2D31C7013B2E9" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_42B288DA57673EE5B9A0D31C70121A07" xlink:to="loc_us-gaap_ExcessTaxBenefitFromShareBasedCompensationOperatingActivities_7B28E5BAF69BCC7149C2D31C7013B2E9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherNoncashIncomeExpense" xlink:label="loc_us-gaap_OtherNoncashIncomeExpense_A0F5069997BF7B6840FBD31C701314D1" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_42B288DA57673EE5B9A0D31C70121A07" xlink:to="loc_us-gaap_OtherNoncashIncomeExpense_A0F5069997BF7B6840FBD31C701314D1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInOtherOperatingAssetsAndLiabilitiesNetAbstract" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherOperatingAssetsAndLiabilitiesNetAbstract_C915B8D1164D762A2650D31C7013C13F" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_9B05992D9BD2E6889C67D31C701216F2" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherOperatingAssetsAndLiabilitiesNetAbstract_C915B8D1164D762A2650D31C7013C13F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInAccountsReceivable" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsReceivable_879E1817CBB8E30B3588D31C7013319A" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOtherOperatingAssetsAndLiabilitiesNetAbstract_C915B8D1164D762A2650D31C7013C13F" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsReceivable_879E1817CBB8E30B3588D31C7013319A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInInventories" xlink:label="loc_us-gaap_IncreaseDecreaseInInventories_47D94A4D360ECEE69470D31C7013E6A2" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOtherOperatingAssetsAndLiabilitiesNetAbstract_C915B8D1164D762A2650D31C7013C13F" xlink:to="loc_us-gaap_IncreaseDecreaseInInventories_47D94A4D360ECEE69470D31C7013E6A2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInDeferredIncomeTaxes" xlink:label="loc_us-gaap_IncreaseDecreaseInDeferredIncomeTaxes_9B8F10B67775955F71ACD31C7013262F" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOtherOperatingAssetsAndLiabilitiesNetAbstract_C915B8D1164D762A2650D31C7013C13F" xlink:to="loc_us-gaap_IncreaseDecreaseInDeferredIncomeTaxes_9B8F10B67775955F71ACD31C7013262F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets" xlink:label="loc_us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_D38E89D91262CEC92AB7D31C701368E5" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOtherOperatingAssetsAndLiabilitiesNetAbstract_C915B8D1164D762A2650D31C7013C13F" xlink:to="loc_us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_D38E89D91262CEC92AB7D31C701368E5" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInOtherOperatingAssets" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherOperatingAssets_19C46D197FDBD4BEA847D31C7013C497" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOtherOperatingAssetsAndLiabilitiesNetAbstract_C915B8D1164D762A2650D31C7013C13F" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherOperatingAssets_19C46D197FDBD4BEA847D31C7013C497" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInAccountsPayable" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsPayable_0B8D4E57D8539E1082EED31C7013A62D" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOtherOperatingAssetsAndLiabilitiesNetAbstract_C915B8D1164D762A2650D31C7013C13F" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsPayable_0B8D4E57D8539E1082EED31C7013A62D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInAccruedLiabilities" xlink:label="loc_us-gaap_IncreaseDecreaseInAccruedLiabilities_32F1D658A62054DB273FD31C701316FB" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOtherOperatingAssetsAndLiabilitiesNetAbstract_C915B8D1164D762A2650D31C7013C13F" xlink:to="loc_us-gaap_IncreaseDecreaseInAccruedLiabilities_32F1D658A62054DB273FD31C701316FB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInOtherNoncurrentLiabilities" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherNoncurrentLiabilities_29FB01FB9AFB1E548D4AD31C7014CEF5" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOtherOperatingAssetsAndLiabilitiesNetAbstract_C915B8D1164D762A2650D31C7013C13F" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherNoncurrentLiabilities_29FB01FB9AFB1E548D4AD31C7014CEF5" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInEmployeeRelatedLiabilities" xlink:label="loc_us-gaap_IncreaseDecreaseInEmployeeRelatedLiabilities_2D04B97D9A372E5397A9D31C701488DD" xlink:type="locator" />
    <definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOtherOperatingAssetsAndLiabilitiesNetAbstract_C915B8D1164D762A2650D31C7013C13F" xlink:to="loc_us-gaap_IncreaseDecreaseInEmployeeRelatedLiabilities_2D04B97D9A372E5397A9D31C701488DD" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInDeferredRevenue" xlink:label="loc_us-gaap_IncreaseDecreaseInDeferredRevenue_D4CE289893C716D803A8D31C70142B99" xlink:type="locator" />
    <definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOtherOperatingAssetsAndLiabilitiesNetAbstract_C915B8D1164D762A2650D31C7013C13F" xlink:to="loc_us-gaap_IncreaseDecreaseInDeferredRevenue_D4CE289893C716D803A8D31C70142B99" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable" xlink:label="loc_us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable_E196E4EE97EC06E81179D31C701447A7" xlink:type="locator" />
    <definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOtherOperatingAssetsAndLiabilitiesNetAbstract_C915B8D1164D762A2650D31C7013C13F" xlink:to="loc_us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable_E196E4EE97EC06E81179D31C701447A7" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_8A5B93C9AF8A09C30A3DD31C701427FF" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_9B05992D9BD2E6889C67D31C701216F2" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_8A5B93C9AF8A09C30A3DD31C701427FF" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_B03B374AD44CF55F547ED31C7014615E" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_FF5A4F619075C45A2242D31C7012FF9A" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_B03B374AD44CF55F547ED31C7014615E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PaymentsToAcquireInvestments" xlink:label="loc_us-gaap_PaymentsToAcquireInvestments_478E6BECA1705E1B6106D31C70147AD9" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_B03B374AD44CF55F547ED31C7014615E" xlink:to="loc_us-gaap_PaymentsToAcquireInvestments_478E6BECA1705E1B6106D31C70147AD9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProceedsFromSaleOfAvailableForSaleSecurities" xlink:label="loc_us-gaap_ProceedsFromSaleOfAvailableForSaleSecurities_8BF0E5DD94F7FD99EBADD31C7014C423" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_B03B374AD44CF55F547ED31C7014615E" xlink:to="loc_us-gaap_ProceedsFromSaleOfAvailableForSaleSecurities_8BF0E5DD94F7FD99EBADD31C7014C423" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities" xlink:label="loc_us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities_E970434E894F933C2928D31C7014B9EE" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_B03B374AD44CF55F547ED31C7014615E" xlink:to="loc_us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities_E970434E894F933C2928D31C7014B9EE" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PaymentsToAcquireProductiveAssets" xlink:label="loc_us-gaap_PaymentsToAcquireProductiveAssets_1E6D4B7C07694339213ED31C70146A92" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_B03B374AD44CF55F547ED31C7014615E" xlink:to="loc_us-gaap_PaymentsToAcquireProductiveAssets_1E6D4B7C07694339213ED31C70146A92" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_49B93534268B5637C771D31C70145D29" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_B03B374AD44CF55F547ED31C7014615E" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_49B93534268B5637C771D31C70145D29" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_13CDB6C926FAD12F8AD6D31C701466EF" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_B03B374AD44CF55F547ED31C7014615E" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_13CDB6C926FAD12F8AD6D31C701466EF" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_C14C71C72CAE55F83190D31C70146263" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_FF5A4F619075C45A2242D31C7012FF9A" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_C14C71C72CAE55F83190D31C70146263" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_07FA935613A6F9006C8DD31C701595AD" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_C14C71C72CAE55F83190D31C70146263" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_07FA935613A6F9006C8DD31C701595AD" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation" xlink:label="loc_us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation_64F8A589F10E5689BE6BD31C70156C26" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_C14C71C72CAE55F83190D31C70146263" xlink:to="loc_us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation_64F8A589F10E5689BE6BD31C70156C26" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ExcessTaxBenefitFromShareBasedCompensationFinancingActivities" xlink:label="loc_us-gaap_ExcessTaxBenefitFromShareBasedCompensationFinancingActivities_20E04E9702E156219A43D31C7015020B" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_C14C71C72CAE55F83190D31C70146263" xlink:to="loc_us-gaap_ExcessTaxBenefitFromShareBasedCompensationFinancingActivities_20E04E9702E156219A43D31C7015020B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PaymentsForRepurchaseOfCommonStock" xlink:label="loc_us-gaap_PaymentsForRepurchaseOfCommonStock_A1D4FE3541BA272AF66CD31C7015EBA9" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_C14C71C72CAE55F83190D31C70146263" xlink:to="loc_us-gaap_PaymentsForRepurchaseOfCommonStock_A1D4FE3541BA272AF66CD31C7015EBA9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_AAA470A0E3205B15D7A6D31C7015D2B3" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_C14C71C72CAE55F83190D31C70146263" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_AAA470A0E3205B15D7A6D31C7015D2B3" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EffectOfExchangeRateOnCashAndCashEquivalents" xlink:label="loc_us-gaap_EffectOfExchangeRateOnCashAndCashEquivalents_6146FF23228B1C8A0F85D31C70154090" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_FF5A4F619075C45A2242D31C7012FF9A" xlink:to="loc_us-gaap_EffectOfExchangeRateOnCashAndCashEquivalents_6146FF23228B1C8A0F85D31C70154090" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease" xlink:label="loc_us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease_37B25119B2F9DF38B1E3D31C7015E7C6" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_FF5A4F619075C45A2242D31C7012FF9A" xlink:to="loc_us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease_37B25119B2F9DF38B1E3D31C7015E7C6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_F607814D0F750173BBC9D31C70153716" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_FF5A4F619075C45A2242D31C7012FF9A" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_F607814D0F750173BBC9D31C70153716" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SupplementalCashFlowInformationAbstract" xlink:label="loc_us-gaap_SupplementalCashFlowInformationAbstract_4EE275822F18EA402A76D31C70158F02" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_FF5A4F619075C45A2242D31C7012FF9A" xlink:to="loc_us-gaap_SupplementalCashFlowInformationAbstract_4EE275822F18EA402A76D31C70158F02" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeTaxesPaidNet" xlink:label="loc_us-gaap_IncomeTaxesPaidNet_58EAA9CD828A8780F7E3D31C701553CD" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SupplementalCashFlowInformationAbstract_4EE275822F18EA402A76D31C70158F02" xlink:to="loc_us-gaap_IncomeTaxesPaidNet_58EAA9CD828A8780F7E3D31C701553CD" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" xlink:label="loc_us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_9B8B334CCEEDDDB456D1D31C70150D8D" xlink:type="locator" />
    <definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_FF5A4F619075C45A2242D31C7012FF9A" xlink:to="loc_us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_9B8B334CCEEDDDB456D1D31C70150D8D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CapitalExpendituresIncurredButNotYetPaid" xlink:label="loc_us-gaap_CapitalExpendituresIncurredButNotYetPaid_CA974BB8BD8B1308CC68D31C70153EF4" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_9B8B334CCEEDDDB456D1D31C70150D8D" xlink:to="loc_us-gaap_CapitalExpendituresIncurredButNotYetPaid_CA974BB8BD8B1308CC68D31C70153EF4" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_LiabilityIncurredforRepurchaseofCommonStock" xlink:label="loc_ftnt_LiabilityIncurredforRepurchaseofCommonStock_921ACDE6336F09B47FBBD31C70162887" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_9B8B334CCEEDDDB456D1D31C70150D8D" xlink:to="loc_ftnt_LiabilityIncurredforRepurchaseofCommonStock_921ACDE6336F09B47FBBD31C70162887" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fortinet.com/role/ConsolidatedStatementsOfComprehensiveIncomeUnaudited" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_1B711588B57C0C8BC01CD31C701A4177" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_D95B20BEE4DCE3ED2795D31C701A92DE" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_1B711588B57C0C8BC01CD31C701A4177" xlink:to="loc_us-gaap_StatementTable_D95B20BEE4DCE3ED2795D31C701A92DE" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementScenarioAxis" xlink:label="loc_us-gaap_StatementScenarioAxis_180CDE6818C0B8E08C27D31C701A66CB" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_D95B20BEE4DCE3ED2795D31C701A92DE" xlink:to="loc_us-gaap_StatementScenarioAxis_180CDE6818C0B8E08C27D31C701A66CB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScenarioUnspecifiedDomain" xlink:label="loc_us-gaap_ScenarioUnspecifiedDomain_2376ACD74B6EF40E4105D31C701AFBE8_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementScenarioAxis_180CDE6818C0B8E08C27D31C701A66CB" xlink:to="loc_us-gaap_ScenarioUnspecifiedDomain_2376ACD74B6EF40E4105D31C701AFBE8_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScenarioUnspecifiedDomain" xlink:label="loc_us-gaap_ScenarioUnspecifiedDomain_2376ACD74B6EF40E4105D31C701AFBE8" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementScenarioAxis_180CDE6818C0B8E08C27D31C701A66CB" xlink:to="loc_us-gaap_ScenarioUnspecifiedDomain_2376ACD74B6EF40E4105D31C701AFBE8" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="loc_us-gaap_NetIncomeLoss_6D0251D084AAC19C671CD31C701AA7B2" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_1B711588B57C0C8BC01CD31C701A4177" xlink:to="loc_us-gaap_NetIncomeLoss_6D0251D084AAC19C671CD31C701AA7B2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParentAbstract" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParentAbstract_36F8BBF1C85A39DF7E92D31C701A0E4F" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_1B711588B57C0C8BC01CD31C701A4177" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParentAbstract_36F8BBF1C85A39DF7E92D31C701A0E4F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentBeforeTaxPortionAttributableToParent" xlink:label="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentBeforeTaxPortionAttributableToParent_5D89EAF079CC9AB37211D31C701A555A" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParentAbstract_36F8BBF1C85A39DF7E92D31C701A0E4F" xlink:to="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentBeforeTaxPortionAttributableToParent_5D89EAF079CC9AB37211D31C701A555A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax" xlink:label="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax_4A6AC876B2BBA47D8ACED31C701AFE76" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParentAbstract_36F8BBF1C85A39DF7E92D31C701A0E4F" xlink:to="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax_4A6AC876B2BBA47D8ACED31C701AFE76" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1_0C11DE619FB174261621D31C701BAEE5" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParentAbstract_36F8BBF1C85A39DF7E92D31C701A0E4F" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1_0C11DE619FB174261621D31C701BAEE5" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_3B452EE4AEBBCA841D52D31C701BF97D" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParentAbstract_36F8BBF1C85A39DF7E92D31C701A0E4F" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_3B452EE4AEBBCA841D52D31C701BF97D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ComprehensiveIncomeNetOfTax" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTax_0482B5D66682B53B56EDD31C701B73E2" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_1B711588B57C0C8BC01CD31C701A4177" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTax_0482B5D66682B53B56EDD31C701B73E2" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fortinet.com/role/ConsolidatedStatementsOfOperationsUnaudited" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_E4475ADBA11299E3A69DD30749737FE4" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_CD2CA0600B3B8583DFD9D3074973E14B" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_E4475ADBA11299E3A69DD30749737FE4" xlink:to="loc_us-gaap_StatementTable_CD2CA0600B3B8583DFD9D3074973E14B" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementScenarioAxis" xlink:label="loc_us-gaap_StatementScenarioAxis_F417B9A33DDDDBAB5A7AD3074973FEFC" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_CD2CA0600B3B8583DFD9D3074973E14B" xlink:to="loc_us-gaap_StatementScenarioAxis_F417B9A33DDDDBAB5A7AD3074973FEFC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScenarioUnspecifiedDomain" xlink:label="loc_us-gaap_ScenarioUnspecifiedDomain_7E3FBFA9CB80B682FC41D3074973B767_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementScenarioAxis_F417B9A33DDDDBAB5A7AD3074973FEFC" xlink:to="loc_us-gaap_ScenarioUnspecifiedDomain_7E3FBFA9CB80B682FC41D3074973B767_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScenarioUnspecifiedDomain" xlink:label="loc_us-gaap_ScenarioUnspecifiedDomain_7E3FBFA9CB80B682FC41D3074973B767" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementScenarioAxis_F417B9A33DDDDBAB5A7AD3074973FEFC" xlink:to="loc_us-gaap_ScenarioUnspecifiedDomain_7E3FBFA9CB80B682FC41D3074973B767" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SalesRevenueNetAbstract" xlink:label="loc_us-gaap_SalesRevenueNetAbstract_45575195AC841C74347CD30749736AE1" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_E4475ADBA11299E3A69DD30749737FE4" xlink:to="loc_us-gaap_SalesRevenueNetAbstract_45575195AC841C74347CD30749736AE1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SalesRevenueGoodsNet" xlink:label="loc_us-gaap_SalesRevenueGoodsNet_7348310C763EEF04847CD3074974686E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SalesRevenueNetAbstract_45575195AC841C74347CD30749736AE1" xlink:to="loc_us-gaap_SalesRevenueGoodsNet_7348310C763EEF04847CD3074974686E" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_SalesRevenueServicesandOtherNet" xlink:label="loc_ftnt_SalesRevenueServicesandOtherNet_E03ABFD5A0C22A169A66D30749748C96" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SalesRevenueNetAbstract_45575195AC841C74347CD30749736AE1" xlink:to="loc_ftnt_SalesRevenueServicesandOtherNet_E03ABFD5A0C22A169A66D30749748C96" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SalesRevenueNet" xlink:label="loc_us-gaap_SalesRevenueNet_7759455A27D6E8A9A430D3074974207B" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SalesRevenueNetAbstract_45575195AC841C74347CD30749736AE1" xlink:to="loc_us-gaap_SalesRevenueNet_7759455A27D6E8A9A430D3074974207B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CostOfGoodsAndServicesSoldAbstract" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSoldAbstract_8461FF3EAFDAB6F66690D30749744492" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_E4475ADBA11299E3A69DD30749737FE4" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSoldAbstract_8461FF3EAFDAB6F66690D30749744492" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CostOfGoodsSold" xlink:label="loc_us-gaap_CostOfGoodsSold_468BA77E0FCD1965FA88D307497424F0" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostOfGoodsAndServicesSoldAbstract_8461FF3EAFDAB6F66690D30749744492" xlink:to="loc_us-gaap_CostOfGoodsSold_468BA77E0FCD1965FA88D307497424F0" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_CostofServicesandOther" xlink:label="loc_ftnt_CostofServicesandOther_4F05BB47EDD75452F208D30749748558" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostOfGoodsAndServicesSoldAbstract_8461FF3EAFDAB6F66690D30749744492" xlink:to="loc_ftnt_CostofServicesandOther_4F05BB47EDD75452F208D30749748558" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CostOfGoodsAndServicesSold" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_2591A6BFA9BA29802446D30749745C4C" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostOfGoodsAndServicesSoldAbstract_8461FF3EAFDAB6F66690D30749744492" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_2591A6BFA9BA29802446D30749745C4C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_GrossProfitAbstract" xlink:label="loc_us-gaap_GrossProfitAbstract_D3B817F62130E78BE739D3074974F3F9" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_E4475ADBA11299E3A69DD30749737FE4" xlink:to="loc_us-gaap_GrossProfitAbstract_D3B817F62130E78BE739D3074974F3F9" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_ProductGrossProfit" xlink:label="loc_ftnt_ProductGrossProfit_078A00F2E2D3F4AF997ED30749740804" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GrossProfitAbstract_D3B817F62130E78BE739D3074974F3F9" xlink:to="loc_ftnt_ProductGrossProfit_078A00F2E2D3F4AF997ED30749740804" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_ServicesandOtherGrossProfit" xlink:label="loc_ftnt_ServicesandOtherGrossProfit_F6CD1CF73319476B5A29D3074974A59A" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GrossProfitAbstract_D3B817F62130E78BE739D3074974F3F9" xlink:to="loc_ftnt_ServicesandOtherGrossProfit_F6CD1CF73319476B5A29D3074974A59A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_GrossProfit" xlink:label="loc_us-gaap_GrossProfit_14C5E4E5428A93826E2AD3074974B0B9" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GrossProfitAbstract_D3B817F62130E78BE739D3074974F3F9" xlink:to="loc_us-gaap_GrossProfit_14C5E4E5428A93826E2AD3074974B0B9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OperatingExpensesAbstract" xlink:label="loc_us-gaap_OperatingExpensesAbstract_9E2E940D3A10C305A3E1D307497497C2" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_E4475ADBA11299E3A69DD30749737FE4" xlink:to="loc_us-gaap_OperatingExpensesAbstract_9E2E940D3A10C305A3E1D307497497C2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ResearchAndDevelopmentExpense" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_F258ACDADE67A491F3A0D307497528BB" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_9E2E940D3A10C305A3E1D307497497C2" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_F258ACDADE67A491F3A0D307497528BB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SellingAndMarketingExpense" xlink:label="loc_us-gaap_SellingAndMarketingExpense_3561C71C21E370F9F4E1D3074975280C" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_9E2E940D3A10C305A3E1D307497497C2" xlink:to="loc_us-gaap_SellingAndMarketingExpense_3561C71C21E370F9F4E1D3074975280C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_GeneralAndAdministrativeExpense" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpense_13D7F572E6B27FD9A9A7D30749757D53" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_9E2E940D3A10C305A3E1D307497497C2" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpense_13D7F572E6B27FD9A9A7D30749757D53" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OperatingExpenses" xlink:label="loc_us-gaap_OperatingExpenses_8DF9108F830EDDAD075AD3074975167E" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_9E2E940D3A10C305A3E1D307497497C2" xlink:to="loc_us-gaap_OperatingExpenses_8DF9108F830EDDAD075AD3074975167E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OperatingIncomeLoss" xlink:label="loc_us-gaap_OperatingIncomeLoss_35D18D3578D0989BED8DD3074975F35A" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_E4475ADBA11299E3A69DD30749737FE4" xlink:to="loc_us-gaap_OperatingIncomeLoss_35D18D3578D0989BED8DD3074975F35A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InvestmentIncomeNet" xlink:label="loc_us-gaap_InvestmentIncomeNet_34B74A21DFD504D6BFB6D307497599A9" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_E4475ADBA11299E3A69DD30749737FE4" xlink:to="loc_us-gaap_InvestmentIncomeNet_34B74A21DFD504D6BFB6D307497599A9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherNonoperatingIncomeExpense" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_58564F189725DCB80523D3074975E8BE" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_E4475ADBA11299E3A69DD30749737FE4" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_58564F189725DCB80523D3074975E8BE" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_9478499AD0ACF103D379D3074975FF91" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_E4475ADBA11299E3A69DD30749737FE4" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_9478499AD0ACF103D379D3074975FF91" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_599AA994CB90D8D753FED30749751B01" xlink:type="locator" />
    <definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_E4475ADBA11299E3A69DD30749737FE4" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_599AA994CB90D8D753FED30749751B01" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="loc_us-gaap_NetIncomeLoss_C95F1BF59CE664C35F4AD3074975A1A1" xlink:type="locator" />
    <definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_E4475ADBA11299E3A69DD30749737FE4" xlink:to="loc_us-gaap_NetIncomeLoss_C95F1BF59CE664C35F4AD3074975A1A1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EarningsPerShareAbstract" xlink:label="loc_us-gaap_EarningsPerShareAbstract_070B5E1B761FBA373FFBD30749759B90" xlink:type="locator" />
    <definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_E4475ADBA11299E3A69DD30749737FE4" xlink:to="loc_us-gaap_EarningsPerShareAbstract_070B5E1B761FBA373FFBD30749759B90" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EarningsPerShareBasic" xlink:label="loc_us-gaap_EarningsPerShareBasic_59121BEAE8C871CBE574D3074975DFB9" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_070B5E1B761FBA373FFBD30749759B90" xlink:to="loc_us-gaap_EarningsPerShareBasic_59121BEAE8C871CBE574D3074975DFB9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EarningsPerShareDiluted" xlink:label="loc_us-gaap_EarningsPerShareDiluted_D9D65BBC28D0042F7DBED3074975FCE9" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_070B5E1B761FBA373FFBD30749759B90" xlink:to="loc_us-gaap_EarningsPerShareDiluted_D9D65BBC28D0042F7DBED3074975FCE9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_0368A7D8FB61142983DAD30749751780" xlink:type="locator" />
    <definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_E4475ADBA11299E3A69DD30749737FE4" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_0368A7D8FB61142983DAD30749751780" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_BD37926DAD39DF4ACCC3D30749764D99" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_0368A7D8FB61142983DAD30749751780" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_BD37926DAD39DF4ACCC3D30749764D99" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_73A9EE5F1E747467C995D30749763204" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_0368A7D8FB61142983DAD30749751780" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_73A9EE5F1E747467C995D30749763204" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fortinet.com/role/DeferredRevenue" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/DeferredRevenueDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredRevenueArrangementLineItems" xlink:label="loc_us-gaap_DeferredRevenueArrangementLineItems_E788A195152506B5D86DAA20D3D45AA2" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredRevenueArrangementByTypeTable" xlink:label="loc_us-gaap_DeferredRevenueArrangementByTypeTable_7B5C1184EFBD465BCE03AA20D3D4A141" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DeferredRevenueArrangementLineItems_E788A195152506B5D86DAA20D3D45AA2" xlink:to="loc_us-gaap_DeferredRevenueArrangementByTypeTable_7B5C1184EFBD465BCE03AA20D3D4A141" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProductOrServiceAxis" xlink:label="loc_us-gaap_ProductOrServiceAxis_D95A5F340F70AB21519BAA20D3D45308" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DeferredRevenueArrangementByTypeTable_7B5C1184EFBD465BCE03AA20D3D4A141" xlink:to="loc_us-gaap_ProductOrServiceAxis_D95A5F340F70AB21519BAA20D3D45308" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProductsAndServicesDomain" xlink:label="loc_us-gaap_ProductsAndServicesDomain_96E4942DBAE9C28B7F36AA20D3D425CE_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ProductOrServiceAxis_D95A5F340F70AB21519BAA20D3D45308" xlink:to="loc_us-gaap_ProductsAndServicesDomain_96E4942DBAE9C28B7F36AA20D3D425CE_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProductsAndServicesDomain" xlink:label="loc_us-gaap_ProductsAndServicesDomain_96E4942DBAE9C28B7F36AA20D3D425CE" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ProductOrServiceAxis_D95A5F340F70AB21519BAA20D3D45308" xlink:to="loc_us-gaap_ProductsAndServicesDomain_96E4942DBAE9C28B7F36AA20D3D425CE" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProductMember" xlink:label="loc_us-gaap_ProductMember_FE95C00E9106F26877EAAA20D3D4BFEC" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_96E4942DBAE9C28B7F36AA20D3D425CE" xlink:to="loc_us-gaap_ProductMember_FE95C00E9106F26877EAAA20D3D4BFEC" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_ServicesMember" xlink:label="loc_ftnt_ServicesMember_A66C09EB3E5D468C88D8AA20D3D40BC6" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_96E4942DBAE9C28B7F36AA20D3D425CE" xlink:to="loc_ftnt_ServicesMember_A66C09EB3E5D468C88D8AA20D3D40BC6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredRevenueCurrent" xlink:label="loc_us-gaap_DeferredRevenueCurrent_FD19E4CD5DC99AE0C1DEAA20D3D42672" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredRevenueArrangementLineItems_E788A195152506B5D86DAA20D3D45AA2" xlink:to="loc_us-gaap_DeferredRevenueCurrent_FD19E4CD5DC99AE0C1DEAA20D3D42672" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredRevenueNoncurrent" xlink:label="loc_us-gaap_DeferredRevenueNoncurrent_562B957551A16728F13EAA20D3D4F4EC" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredRevenueArrangementLineItems_E788A195152506B5D86DAA20D3D45AA2" xlink:to="loc_us-gaap_DeferredRevenueNoncurrent_562B957551A16728F13EAA20D3D4F4EC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredRevenue" xlink:label="loc_us-gaap_DeferredRevenue_B78E0E8D06A55E21B996AA20D3D4EE2C" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredRevenueArrangementLineItems_E788A195152506B5D86DAA20D3D45AA2" xlink:to="loc_us-gaap_DeferredRevenue_B78E0E8D06A55E21B996AA20D3D4EE2C" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fortinet.com/role/DeferredRevenueTables" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/DocumentAndEntityInformation" xlink:type="extended">
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_DocumentInformationLineItems" xlink:label="loc_dei_DocumentInformationLineItems_637C723BC81A806092F7A92D80DFB2D4" xlink:type="locator" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_DocumentInformationTable" xlink:label="loc_dei_DocumentInformationTable_C591586B639C0438757AA92D80DF1B5F" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_DocumentInformationLineItems_637C723BC81A806092F7A92D80DFB2D4" xlink:to="loc_dei_DocumentInformationTable_C591586B639C0438757AA92D80DF1B5F" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_DocumentInformationDocumentAxis" xlink:label="loc_dei_DocumentInformationDocumentAxis_F8F682EA45DBD00DE0DFA92D80DFD9D9" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_DocumentInformationTable_C591586B639C0438757AA92D80DF1B5F" xlink:to="loc_dei_DocumentInformationDocumentAxis_F8F682EA45DBD00DE0DFA92D80DFD9D9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_DocumentDomain" xlink:label="loc_dei_DocumentDomain_F522EE5A633E06EAF1ACA92D80DF7C90_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_DocumentInformationDocumentAxis_F8F682EA45DBD00DE0DFA92D80DFD9D9" xlink:to="loc_dei_DocumentDomain_F522EE5A633E06EAF1ACA92D80DF7C90_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_DocumentDomain" xlink:label="loc_dei_DocumentDomain_F522EE5A633E06EAF1ACA92D80DF7C90" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_DocumentInformationDocumentAxis_F8F682EA45DBD00DE0DFA92D80DFD9D9" xlink:to="loc_dei_DocumentDomain_F522EE5A633E06EAF1ACA92D80DF7C90" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_EntityRegistrantName" xlink:label="loc_dei_EntityRegistrantName_14AD6E9D8B7D12ADE7B3A92D80DFAB9B" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_637C723BC81A806092F7A92D80DFB2D4" xlink:to="loc_dei_EntityRegistrantName_14AD6E9D8B7D12ADE7B3A92D80DFAB9B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_EntityCentralIndexKey" xlink:label="loc_dei_EntityCentralIndexKey_384756870828E48A397AA92D80DF38F8" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_637C723BC81A806092F7A92D80DFB2D4" xlink:to="loc_dei_EntityCentralIndexKey_384756870828E48A397AA92D80DF38F8" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_DocumentType" xlink:label="loc_dei_DocumentType_AE7615F99CB2B982E547A92D80DF7E1B" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_637C723BC81A806092F7A92D80DFB2D4" xlink:to="loc_dei_DocumentType_AE7615F99CB2B982E547A92D80DF7E1B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_DocumentPeriodEndDate" xlink:label="loc_dei_DocumentPeriodEndDate_CEF5DD760865FB664AEBA92D80DF7571" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_637C723BC81A806092F7A92D80DFB2D4" xlink:to="loc_dei_DocumentPeriodEndDate_CEF5DD760865FB664AEBA92D80DF7571" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_AmendmentFlag" xlink:label="loc_dei_AmendmentFlag_00266D48F175FBF56873A92D80DF20AC" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_637C723BC81A806092F7A92D80DFB2D4" xlink:to="loc_dei_AmendmentFlag_00266D48F175FBF56873A92D80DF20AC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_DocumentFiscalYearFocus" xlink:label="loc_dei_DocumentFiscalYearFocus_2BFB33451B02886E17AEA92D80DF43A3" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_637C723BC81A806092F7A92D80DFB2D4" xlink:to="loc_dei_DocumentFiscalYearFocus_2BFB33451B02886E17AEA92D80DF43A3" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_DocumentFiscalPeriodFocus" xlink:label="loc_dei_DocumentFiscalPeriodFocus_3B2722E2A30AFBE12DBDA92D80DFF3D9" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_637C723BC81A806092F7A92D80DFB2D4" xlink:to="loc_dei_DocumentFiscalPeriodFocus_3B2722E2A30AFBE12DBDA92D80DFF3D9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_CurrentFiscalYearEndDate" xlink:label="loc_dei_CurrentFiscalYearEndDate_2A8069907D7F3A99D809A92D80DFB2E1" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_637C723BC81A806092F7A92D80DFB2D4" xlink:to="loc_dei_CurrentFiscalYearEndDate_2A8069907D7F3A99D809A92D80DFB2E1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_EntityCurrentReportingStatus" xlink:label="loc_dei_EntityCurrentReportingStatus_74F27F878DC5120E7E90A92D80DFC494" xlink:type="locator" />
    <definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_637C723BC81A806092F7A92D80DFB2D4" xlink:to="loc_dei_EntityCurrentReportingStatus_74F27F878DC5120E7E90A92D80DFC494" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_EntityFilerCategory" xlink:label="loc_dei_EntityFilerCategory_7A305C61A4E94DF54354A92D80DF8C2F" xlink:type="locator" />
    <definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_637C723BC81A806092F7A92D80DFB2D4" xlink:to="loc_dei_EntityFilerCategory_7A305C61A4E94DF54354A92D80DF8C2F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_EntityCommonStockSharesOutstanding" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_DE30C0DD1A181673108BA92D80E909D2" xlink:type="locator" />
    <definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_637C723BC81A806092F7A92D80DFB2D4" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_DE30C0DD1A181673108BA92D80E909D2" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fortinet.com/role/EmployeeBenefitPlan" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/EmployeeBenefitPlanDetails" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/FinancialInstrumentsAndFairValue" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/FinancialInstrumentsAndFairValueChangeToContingentConsiderationLiabilityDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_B4C8C2D26C5F4DFA433EAE5F6B2C4702" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_56CF131D336DC1C3AFFAAE5F6B2B8F7C" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_B4C8C2D26C5F4DFA433EAE5F6B2C4702" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_56CF131D336DC1C3AFFAAE5F6B2B8F7C" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueByMeasurementBasisAxis" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_A9DD280AD81DA9964B00AE60095E91B8" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_56CF131D336DC1C3AFFAAE5F6B2B8F7C" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_A9DD280AD81DA9964B00AE60095E91B8" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueDisclosureItemAmountsDomain" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_727CE1D4A4454E2EB14FAE600A2C8137_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_A9DD280AD81DA9964B00AE60095E91B8" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_727CE1D4A4454E2EB14FAE600A2C8137_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueDisclosureItemAmountsDomain" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_727CE1D4A4454E2EB14FAE600A2C8137" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_A9DD280AD81DA9964B00AE60095E91B8" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_727CE1D4A4454E2EB14FAE600A2C8137" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_4DF88C4A815BA1CDE312AE6009AD1140" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_727CE1D4A4454E2EB14FAE600A2C8137" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_4DF88C4A815BA1CDE312AE6009AD1140" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_C2BE206487784F15D5A3AE5F6B2C83D7" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_56CF131D336DC1C3AFFAAE5F6B2B8F7C" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_C2BE206487784F15D5A3AE5F6B2C83D7" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_F2762895362E8F835535AE5F6B2C4DF4_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_C2BE206487784F15D5A3AE5F6B2C83D7" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_F2762895362E8F835535AE5F6B2C4DF4_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_F2762895362E8F835535AE5F6B2C4DF4" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_C2BE206487784F15D5A3AE5F6B2C83D7" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_F2762895362E8F835535AE5F6B2C4DF4" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueMeasurementsRecurringMember" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_FE3462B4D4552D28C5D8AE6009197A03" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_F2762895362E8F835535AE5F6B2C4DF4" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_FE3462B4D4552D28C5D8AE6009197A03" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_MovementinContingentConsiderationLiabilityRollForward" xlink:label="loc_ftnt_MovementinContingentConsiderationLiabilityRollForward_EBB39E569E7D6D327AD8AE64B4EE1D85" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_B4C8C2D26C5F4DFA433EAE5F6B2C4702" xlink:to="loc_ftnt_MovementinContingentConsiderationLiabilityRollForward_EBB39E569E7D6D327AD8AE64B4EE1D85" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationLiability" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_963A568B52068F65A7A8AE60081EC80C" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ftnt_MovementinContingentConsiderationLiabilityRollForward_EBB39E569E7D6D327AD8AE64B4EE1D85" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_963A568B52068F65A7A8AE60081EC80C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1_479756B2E222B44FE477AE61BB0B3FC8" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ftnt_MovementinContingentConsiderationLiabilityRollForward_EBB39E569E7D6D327AD8AE64B4EE1D85" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1_479756B2E222B44FE477AE61BB0B3FC8" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fortinet.com/role/FinancialInstrumentsAndFairValueFairValueMeasurementsDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_8BB43A7ADCD2290C0ED6D387B8DC9FFF" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_E31F3F27AFCC01A401C7D387B8D8C20D" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_8BB43A7ADCD2290C0ED6D387B8DC9FFF" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_E31F3F27AFCC01A401C7D387B8D8C20D" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueByLiabilityClassAxis" xlink:label="loc_us-gaap_FairValueByLiabilityClassAxis_7F2E02E49FB9B4597454D387B8D8F973" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_E31F3F27AFCC01A401C7D387B8D8C20D" xlink:to="loc_us-gaap_FairValueByLiabilityClassAxis_7F2E02E49FB9B4597454D387B8D8F973" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_459E802D6971AE3E0EA7D387B8D84083_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_7F2E02E49FB9B4597454D387B8D8F973" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_459E802D6971AE3E0EA7D387B8D84083_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_459E802D6971AE3E0EA7D387B8D84083" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_7F2E02E49FB9B4597454D387B8D8F973" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_459E802D6971AE3E0EA7D387B8D84083" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_ContingentLiabilityMember" xlink:label="loc_ftnt_ContingentLiabilityMember_E5ADCFACAA90D2150C1BD387B8D8E9E9" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_459E802D6971AE3E0EA7D387B8D84083" xlink:to="loc_ftnt_ContingentLiabilityMember_E5ADCFACAA90D2150C1BD387B8D8E9E9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_8F2D52BA95643FA77ED2D387B8D846D0" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_E31F3F27AFCC01A401C7D387B8D8C20D" xlink:to="loc_us-gaap_RangeAxis_8F2D52BA95643FA77ED2D387B8D846D0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_022FB1256C163A0B34AED387B8D8FB35_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_8F2D52BA95643FA77ED2D387B8D846D0" xlink:to="loc_us-gaap_RangeMember_022FB1256C163A0B34AED387B8D8FB35_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_022FB1256C163A0B34AED387B8D8FB35" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_8F2D52BA95643FA77ED2D387B8D846D0" xlink:to="loc_us-gaap_RangeMember_022FB1256C163A0B34AED387B8D8FB35" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember_EFEDD3C6FFECE5A61565D387B8D86511" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_022FB1256C163A0B34AED387B8D8FB35" xlink:to="loc_us-gaap_MinimumMember_EFEDD3C6FFECE5A61565D387B8D86511" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember_5BB2E94463BFD609F255D387B8D8795B" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_022FB1256C163A0B34AED387B8D8FB35" xlink:to="loc_us-gaap_MaximumMember_5BB2E94463BFD609F255D387B8D8795B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ValuationTechniqueAxis" xlink:label="loc_us-gaap_ValuationTechniqueAxis_791ECE6BE75D1779ABB8D387B8D85C4B" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_E31F3F27AFCC01A401C7D387B8D8C20D" xlink:to="loc_us-gaap_ValuationTechniqueAxis_791ECE6BE75D1779ABB8D387B8D85C4B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ValuationTechniqueDomain" xlink:label="loc_us-gaap_ValuationTechniqueDomain_9650CF2FD333348F603FD387B8D83CC5_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ValuationTechniqueAxis_791ECE6BE75D1779ABB8D387B8D85C4B" xlink:to="loc_us-gaap_ValuationTechniqueDomain_9650CF2FD333348F603FD387B8D83CC5_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ValuationTechniqueDomain" xlink:label="loc_us-gaap_ValuationTechniqueDomain_9650CF2FD333348F603FD387B8D83CC5" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ValuationTechniqueAxis_791ECE6BE75D1779ABB8D387B8D85C4B" xlink:to="loc_us-gaap_ValuationTechniqueDomain_9650CF2FD333348F603FD387B8D83CC5" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeApproachValuationTechniqueMember" xlink:label="loc_us-gaap_IncomeApproachValuationTechniqueMember_405194605FDDCF3622C7D387B8D87C3F" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationTechniqueDomain_9650CF2FD333348F603FD387B8D83CC5" xlink:to="loc_us-gaap_IncomeApproachValuationTechniqueMember_405194605FDDCF3622C7D387B8D87C3F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueByMeasurementBasisAxis" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_69EFCF8A0048DF78CFEDD387B8D8421D" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_E31F3F27AFCC01A401C7D387B8D8C20D" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_69EFCF8A0048DF78CFEDD387B8D8421D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueDisclosureItemAmountsDomain" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_BB9258303869BB9AFD74D387B8DA25D6_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_69EFCF8A0048DF78CFEDD387B8D8421D" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_BB9258303869BB9AFD74D387B8DA25D6_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueDisclosureItemAmountsDomain" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_BB9258303869BB9AFD74D387B8DA25D6" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_69EFCF8A0048DF78CFEDD387B8D8421D" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_BB9258303869BB9AFD74D387B8DA25D6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_F89087DBBA13EBBFDA27D387B8DA7E82" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_BB9258303869BB9AFD74D387B8DA25D6" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_F89087DBBA13EBBFDA27D387B8DA7E82" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember" xlink:label="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_8DD30B9F436D6F32EAC9D387B8DAC21D" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_BB9258303869BB9AFD74D387B8DA25D6" xlink:to="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_8DD30B9F436D6F32EAC9D387B8DAC21D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_4B3F596799D77A63E9C2D387B8DABA52" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_E31F3F27AFCC01A401C7D387B8D8C20D" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_4B3F596799D77A63E9C2D387B8DABA52" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_717EAAF93EC72AA2C885D387B8DA495B_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_4B3F596799D77A63E9C2D387B8DABA52" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_717EAAF93EC72AA2C885D387B8DA495B_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_717EAAF93EC72AA2C885D387B8DA495B" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_4B3F596799D77A63E9C2D387B8DABA52" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_717EAAF93EC72AA2C885D387B8DA495B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_USTreasuryAndGovernmentMember" xlink:label="loc_us-gaap_USTreasuryAndGovernmentMember_3E9F1E53632030ECFD54D387B8DAB64C" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_717EAAF93EC72AA2C885D387B8DA495B" xlink:to="loc_us-gaap_USTreasuryAndGovernmentMember_3E9F1E53632030ECFD54D387B8DAB64C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CorporateDebtSecuritiesMember" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_B88D695C27A7D2570446D387B8DA70D6" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_717EAAF93EC72AA2C885D387B8DA495B" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_B88D695C27A7D2570446D387B8DA70D6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommercialPaperNotIncludedWithCashAndCashEquivalentsMember" xlink:label="loc_us-gaap_CommercialPaperNotIncludedWithCashAndCashEquivalentsMember_963BE6ED68934A980D08D387B8DA74AD" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_717EAAF93EC72AA2C885D387B8DA495B" xlink:to="loc_us-gaap_CommercialPaperNotIncludedWithCashAndCashEquivalentsMember_963BE6ED68934A980D08D387B8DA74AD" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_USStatesAndPoliticalSubdivisionsMember" xlink:label="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_FCD477F977394F6C4E23D387B8DA7E4E" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_717EAAF93EC72AA2C885D387B8DA495B" xlink:to="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_FCD477F977394F6C4E23D387B8DA7E4E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CertificatesOfDepositMember" xlink:label="loc_us-gaap_CertificatesOfDepositMember_D3660B81D9ED95AEF251D387B8DA4D47" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_717EAAF93EC72AA2C885D387B8DA495B" xlink:to="loc_us-gaap_CertificatesOfDepositMember_D3660B81D9ED95AEF251D387B8DA4D47" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_MoneyMarketFundsExcludingCommercialPaperMember" xlink:label="loc_ftnt_MoneyMarketFundsExcludingCommercialPaperMember_B0B3F3C621E17F068F1ED387B8DA4B9C" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_717EAAF93EC72AA2C885D387B8DA495B" xlink:to="loc_ftnt_MoneyMarketFundsExcludingCommercialPaperMember_B0B3F3C621E17F068F1ED387B8DA4B9C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_7F7920ACB52BB01E20F8D387B8DB1A15" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_E31F3F27AFCC01A401C7D387B8D8C20D" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_7F7920ACB52BB01E20F8D387B8DB1A15" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_6E3C2F7791A8D0260C4ED387B8DBE3D5_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_7F7920ACB52BB01E20F8D387B8DB1A15" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_6E3C2F7791A8D0260C4ED387B8DBE3D5_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_6E3C2F7791A8D0260C4ED387B8DBE3D5" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_7F7920ACB52BB01E20F8D387B8DB1A15" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_6E3C2F7791A8D0260C4ED387B8DBE3D5" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueMeasurementsRecurringMember" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_04B530CC57A0D6DCF620D387B8DB32D3" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_6E3C2F7791A8D0260C4ED387B8DBE3D5" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_04B530CC57A0D6DCF620D387B8DB32D3" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BalanceSheetLocationAxis" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_F8C623A0149EE52E1B2CD387B8DB5C44" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_E31F3F27AFCC01A401C7D387B8D8C20D" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_F8C623A0149EE52E1B2CD387B8DB5C44" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BalanceSheetLocationDomain" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_42CF28179754BD99F378D387B8DB114B_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_F8C623A0149EE52E1B2CD387B8DB5C44" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_42CF28179754BD99F378D387B8DB114B_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BalanceSheetLocationDomain" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_42CF28179754BD99F378D387B8DB114B" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_F8C623A0149EE52E1B2CD387B8DB5C44" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_42CF28179754BD99F378D387B8DB114B" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_CashEquivalentsLineItemMember" xlink:label="loc_ftnt_CashEquivalentsLineItemMember_612D981E5DC89AB7C0AED387B8DB3251" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_42CF28179754BD99F378D387B8DB114B" xlink:to="loc_ftnt_CashEquivalentsLineItemMember_612D981E5DC89AB7C0AED387B8DB3251" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_ShortTermInvestmentsLineItemMember" xlink:label="loc_ftnt_ShortTermInvestmentsLineItemMember_8E423F0EBF60FDD67F0FD387B8DB6AB6" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_42CF28179754BD99F378D387B8DB114B" xlink:to="loc_ftnt_ShortTermInvestmentsLineItemMember_8E423F0EBF60FDD67F0FD387B8DB6AB6" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_LongTermInvestmentsLineItemMember" xlink:label="loc_ftnt_LongTermInvestmentsLineItemMember_6AF50846CE029C11D4DBD387B8DB2A09" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_42CF28179754BD99F378D387B8DB114B" xlink:to="loc_ftnt_LongTermInvestmentsLineItemMember_6AF50846CE029C11D4DBD387B8DB2A09" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_0B709DC6B9CDBF8DFEBCD387B8DB2CAF" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_E31F3F27AFCC01A401C7D387B8D8C20D" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_0B709DC6B9CDBF8DFEBCD387B8DB2CAF" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_E1EB681F35FAB0A80A08D387B8DB184B_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_0B709DC6B9CDBF8DFEBCD387B8DB2CAF" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_E1EB681F35FAB0A80A08D387B8DB184B_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_E1EB681F35FAB0A80A08D387B8DB184B" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_0B709DC6B9CDBF8DFEBCD387B8DB2CAF" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_E1EB681F35FAB0A80A08D387B8DB184B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_987222058CFE17C90461D387B8DB4CA8" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_E1EB681F35FAB0A80A08D387B8DB184B" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_987222058CFE17C90461D387B8DB4CA8" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_C5655CAE7BA499CBF55ED387B8DB8BAD" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_E1EB681F35FAB0A80A08D387B8DB184B" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_C5655CAE7BA499CBF55ED387B8DB8BAD" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_BB741A007A38253F278BD387B8DC5B15" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_E1EB681F35FAB0A80A08D387B8DB184B" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_BB741A007A38253F278BD387B8DC5B15" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AvailableForSaleSecurities" xlink:label="loc_us-gaap_AvailableForSaleSecurities_9ACD5A8C4BFBED08951AD387B8DC3A4D" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_8BB43A7ADCD2290C0ED6D387B8DC9FFF" xlink:to="loc_us-gaap_AvailableForSaleSecurities_9ACD5A8C4BFBED08951AD387B8DC3A4D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AssetsFairValueDisclosure" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_1825CC6BF5C0E1EEFAD3D387B8DCE772" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_8BB43A7ADCD2290C0ED6D387B8DC9FFF" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_1825CC6BF5C0E1EEFAD3D387B8DCE772" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationLiability" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_24C2A067CF645046F2AED387B8DCF91F" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_8BB43A7ADCD2290C0ED6D387B8DC9FFF" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_24C2A067CF645046F2AED387B8DCF91F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FinancialLiabilitiesFairValueDisclosure" xlink:label="loc_us-gaap_FinancialLiabilitiesFairValueDisclosure_1003BA3EEF0D828953C4D387B8DC2AFA" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_8BB43A7ADCD2290C0ED6D387B8DC9FFF" xlink:to="loc_us-gaap_FinancialLiabilitiesFairValueDisclosure_1003BA3EEF0D828953C4D387B8DC2AFA" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_FairValueInputsRevenue" xlink:label="loc_ftnt_FairValueInputsRevenue_9F9C7E824148315D8794D387B8DCF558" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_8BB43A7ADCD2290C0ED6D387B8DC9FFF" xlink:to="loc_ftnt_FairValueInputsRevenue_9F9C7E824148315D8794D387B8DCF558" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_FairValueInputsProbabilityofOccurrence" xlink:label="loc_ftnt_FairValueInputsProbabilityofOccurrence_6FA6018B4A54921D9620D387B8DC6ABF" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_8BB43A7ADCD2290C0ED6D387B8DC9FFF" xlink:to="loc_ftnt_FairValueInputsProbabilityofOccurrence_6FA6018B4A54921D9620D387B8DC6ABF" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fortinet.com/role/FinancialInstrumentsAndFairValueInvestmentsDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:label="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_7333BE712CC6F4B09755AFA8BC514D14" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesTable" xlink:label="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesTable_5B663A80762705918134AFA8BC50F2EE" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_7333BE712CC6F4B09755AFA8BC514D14" xlink:to="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesTable_5B663A80762705918134AFA8BC50F2EE" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_7C307E39B2C61C3C7379AFA8BC50B813" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesTable_5B663A80762705918134AFA8BC50F2EE" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_7C307E39B2C61C3C7379AFA8BC50B813" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_87ECC313F879E1CCA938AFA8BC506C74_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_7C307E39B2C61C3C7379AFA8BC50B813" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_87ECC313F879E1CCA938AFA8BC506C74_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_87ECC313F879E1CCA938AFA8BC506C74" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_7C307E39B2C61C3C7379AFA8BC50B813" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_87ECC313F879E1CCA938AFA8BC506C74" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_USTreasuryAndGovernmentMember" xlink:label="loc_us-gaap_USTreasuryAndGovernmentMember_BB25CEF2CCFAA2DF7DADAFA8BC50D669" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_87ECC313F879E1CCA938AFA8BC506C74" xlink:to="loc_us-gaap_USTreasuryAndGovernmentMember_BB25CEF2CCFAA2DF7DADAFA8BC50D669" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CorporateDebtSecuritiesMember" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_023475915321BF04F379AFA8BC508A29" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_87ECC313F879E1CCA938AFA8BC506C74" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_023475915321BF04F379AFA8BC508A29" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommercialPaperNotIncludedWithCashAndCashEquivalentsMember" xlink:label="loc_us-gaap_CommercialPaperNotIncludedWithCashAndCashEquivalentsMember_6517059126302EA24A44AFA8BC50E396" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_87ECC313F879E1CCA938AFA8BC506C74" xlink:to="loc_us-gaap_CommercialPaperNotIncludedWithCashAndCashEquivalentsMember_6517059126302EA24A44AFA8BC50E396" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MunicipalBondsMember" xlink:label="loc_us-gaap_MunicipalBondsMember_EB03CDDBB7E898249FDEAFA8BC513440" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_87ECC313F879E1CCA938AFA8BC506C74" xlink:to="loc_us-gaap_MunicipalBondsMember_EB03CDDBB7E898249FDEAFA8BC513440" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CertificatesOfDepositMember" xlink:label="loc_us-gaap_CertificatesOfDepositMember_646D280AD20875750219AFA8BC519831" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_87ECC313F879E1CCA938AFA8BC506C74" xlink:to="loc_us-gaap_CertificatesOfDepositMember_646D280AD20875750219AFA8BC519831" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_USStatesAndPoliticalSubdivisionsMember" xlink:label="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_9D15CE7564B83F7670A8AFA8BC51A5D2" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_87ECC313F879E1CCA938AFA8BC506C74" xlink:to="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_9D15CE7564B83F7670A8AFA8BC51A5D2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_596571D7E0E0423B31B7AFA8BC511DFA" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_7333BE712CC6F4B09755AFA8BC514D14" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_596571D7E0E0423B31B7AFA8BC511DFA" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_AvailableforsaleDebtSecuritiesAccumulatedGrossUnrealizedGainbeforeTax" xlink:label="loc_ftnt_AvailableforsaleDebtSecuritiesAccumulatedGrossUnrealizedGainbeforeTax_845C0D5D3F1398B2B7F1AFA8BC519EE6" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_7333BE712CC6F4B09755AFA8BC514D14" xlink:to="loc_ftnt_AvailableforsaleDebtSecuritiesAccumulatedGrossUnrealizedGainbeforeTax_845C0D5D3F1398B2B7F1AFA8BC519EE6" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_AvailableforsaleDebtSecuritiesAccumulatedGrossUnrealizedLossbeforeTax" xlink:label="loc_ftnt_AvailableforsaleDebtSecuritiesAccumulatedGrossUnrealizedLossbeforeTax_73FAB41870CF418DB927AFA8BC510E16" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_7333BE712CC6F4B09755AFA8BC514D14" xlink:to="loc_ftnt_AvailableforsaleDebtSecuritiesAccumulatedGrossUnrealizedLossbeforeTax_73FAB41870CF418DB927AFA8BC510E16" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_D38243461D5A43E5EC6CAFA8BC51D41C" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_7333BE712CC6F4B09755AFA8BC514D14" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_D38243461D5A43E5EC6CAFA8BC51D41C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAbstract" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAbstract_1DCDE7F02C13209F4973AFA8BC5162E8" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_7333BE712CC6F4B09755AFA8BC514D14" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAbstract_1DCDE7F02C13209F4973AFA8BC5162E8" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue_0D9E2FEC0CC8C623DB65AFA8BC511CF8" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAbstract_1DCDE7F02C13209F4973AFA8BC5162E8" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue_0D9E2FEC0CC8C623DB65AFA8BC511CF8" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_AvailableforsaleSecuritiesContinuousUnrealizedLossPositionLessthan12MonthsAccumulatedLoss" xlink:label="loc_ftnt_AvailableforsaleSecuritiesContinuousUnrealizedLossPositionLessthan12MonthsAccumulatedLoss_88F10AE1D44391C5456FAFA8BC517ACA" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAbstract_1DCDE7F02C13209F4973AFA8BC5162E8" xlink:to="loc_ftnt_AvailableforsaleSecuritiesContinuousUnrealizedLossPositionLessthan12MonthsAccumulatedLoss_88F10AE1D44391C5456FAFA8BC517ACA" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue_6B57CDDAAA51346BA349AFA8BC5143C9" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAbstract_1DCDE7F02C13209F4973AFA8BC5162E8" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue_6B57CDDAAA51346BA349AFA8BC5143C9" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_AvailableforsaleSecuritiesContinuousUnrealizedLossPosition12MonthsorLongerAccumulatedLoss" xlink:label="loc_ftnt_AvailableforsaleSecuritiesContinuousUnrealizedLossPosition12MonthsorLongerAccumulatedLoss_5479B92731C50B40D0B4AFA8BC5100EB" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAbstract_1DCDE7F02C13209F4973AFA8BC5162E8" xlink:to="loc_ftnt_AvailableforsaleSecuritiesContinuousUnrealizedLossPosition12MonthsorLongerAccumulatedLoss_5479B92731C50B40D0B4AFA8BC5100EB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue_8E13C5DBE48F71C3F1D8AFA8BC51AE28" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAbstract_1DCDE7F02C13209F4973AFA8BC5162E8" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue_8E13C5DBE48F71C3F1D8AFA8BC51AE28" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_AvailableforsaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss" xlink:label="loc_ftnt_AvailableforsaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss_8E672764D52529295B9DAFA8BC516632" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAbstract_1DCDE7F02C13209F4973AFA8BC5162E8" xlink:to="loc_ftnt_AvailableforsaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss_8E672764D52529295B9DAFA8BC516632" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract_73352B895862353F6D56AFA8BC528B97" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_7333BE712CC6F4B09755AFA8BC514D14" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract_73352B895862353F6D56AFA8BC528B97" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue_ED6E9F741749245CB5C7AFA8BC524F3D" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract_73352B895862353F6D56AFA8BC528B97" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue_ED6E9F741749245CB5C7AFA8BC524F3D" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_AvailableForSaleSecuritiesDebtMaturitiesAfterOneYearFairValue" xlink:label="loc_ftnt_AvailableForSaleSecuritiesDebtMaturitiesAfterOneYearFairValue_5776DEC44E44561D52CAAFA8BC52E647" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract_73352B895862353F6D56AFA8BC528B97" xlink:to="loc_ftnt_AvailableForSaleSecuritiesDebtMaturitiesAfterOneYearFairValue_5776DEC44E44561D52CAAFA8BC52E647" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fortinet.com/role/FinancialInstrumentsAndFairValueTables" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/ForeignCurrencyDerivatives" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/ForeignCurrencyDerivativesDetails" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/ForeignCurrencyDerivativesTables" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/GoodwillAndOtherIntangibleAssetsnet" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/GoodwillAndOtherIntangibleAssetsnetFiniteLivedIntangibleAssetsDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_46D679E4879EC6E20385B4779AD7616C" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_2749745C407C37981A81B4779ACDF7B7" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_46D679E4879EC6E20385B4779AD7616C" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_2749745C407C37981A81B4779ACDF7B7" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_108009CE44BF690F4B09B4779ACDAB1B" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_2749745C407C37981A81B4779ACDF7B7" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_108009CE44BF690F4B09B4779ACDAB1B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_37BE22F4DD5E7B9F0E1BB4779ACDB641_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_108009CE44BF690F4B09B4779ACDAB1B" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_37BE22F4DD5E7B9F0E1BB4779ACDB641_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_37BE22F4DD5E7B9F0E1BB4779ACDB641" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_108009CE44BF690F4B09B4779ACDAB1B" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_37BE22F4DD5E7B9F0E1BB4779ACDB641" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DevelopedTechnologyRightsMember" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_180FFBF88F506B751804B4779ACD0B49" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_37BE22F4DD5E7B9F0E1BB4779ACDB641" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_180FFBF88F506B751804B4779ACD0B49" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CustomerRelationshipsMember" xlink:label="loc_us-gaap_CustomerRelationshipsMember_1FC1097B0F135B8AA6BEB4779ACDC96C" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_37BE22F4DD5E7B9F0E1BB4779ACDB641" xlink:to="loc_us-gaap_CustomerRelationshipsMember_1FC1097B0F135B8AA6BEB4779ACDC96C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsNetAbstract" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_2DA5B5A6595B442D0C6FB4779AD78413" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_46D679E4879EC6E20385B4779AD7616C" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_2DA5B5A6595B442D0C6FB4779AD78413" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsGross" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_BFC00A20DECE1F32E8F7B4779AD742F9" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_2DA5B5A6595B442D0C6FB4779AD78413" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_BFC00A20DECE1F32E8F7B4779AD742F9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_38C2634A6E3F9BE7FC0DB4779AD78610" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_2DA5B5A6595B442D0C6FB4779AD78413" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_38C2634A6E3F9BE7FC0DB4779AD78610" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsNet" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_52BB5C76AEA754845633B4779AD7255F" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_2DA5B5A6595B442D0C6FB4779AD78413" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_52BB5C76AEA754845633B4779AD7255F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AmortizationOfIntangibleAssets" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_9CE1BD1FD03E3B0F6A74B4779AD7BB46" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_46D679E4879EC6E20385B4779AD7616C" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_9CE1BD1FD03E3B0F6A74B4779AD7BB46" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_5EB4F946598714277724B4779AD7D247" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_46D679E4879EC6E20385B4779AD7616C" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_5EB4F946598714277724B4779AD7D247" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear_C01CA43A5B50FDF363D2B4779AD74A96" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_5EB4F946598714277724B4779AD7D247" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear_C01CA43A5B50FDF363D2B4779AD74A96" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_391C6CFAC3E197821A94B4779AD7CFE6" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_5EB4F946598714277724B4779AD7D247" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_391C6CFAC3E197821A94B4779AD7CFE6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_88CF928C4A140DEECD60B4779AD74FD9" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_5EB4F946598714277724B4779AD7D247" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_88CF928C4A140DEECD60B4779AD74FD9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_4F31BFAE77C81A7DDDC4B4779AD72A2D" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_5EB4F946598714277724B4779AD7D247" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_4F31BFAE77C81A7DDDC4B4779AD72A2D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive_1BAC8C6CF9A010B4CD4BB4779AD70473" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_5EB4F946598714277724B4779AD7D247" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive_1BAC8C6CF9A010B4CD4BB4779AD70473" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive_A5FA945BF197BC3817ACB4779AD7A794" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_5EB4F946598714277724B4779AD7D247" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive_A5FA945BF197BC3817ACB4779AD7A794" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fortinet.com/role/GoodwillAndOtherIntangibleAssetsnetGoodwillDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_D3AA8E3C647C27BB4D4FB4779B3B25D2" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_52C641B8E3CAA2802271B4779B3123F0" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D3AA8E3C647C27BB4D4FB4779B3B25D2" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_52C641B8E3CAA2802271B4779B3123F0" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_48E5938F46516ABCA555B4779B3B2435" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_52C641B8E3CAA2802271B4779B3123F0" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_48E5938F46516ABCA555B4779B3B2435" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_969335AD25B06162A311B4779B3B2B86_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_48E5938F46516ABCA555B4779B3B2435" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_969335AD25B06162A311B4779B3B2B86_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_969335AD25B06162A311B4779B3B2B86" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_48E5938F46516ABCA555B4779B3B2435" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_969335AD25B06162A311B4779B3B2B86" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_CoyotePointSystemsInc.Member" xlink:label="loc_ftnt_CoyotePointSystemsInc.Member_EFD4AE958DC568126EADB4779B3B016F" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_969335AD25B06162A311B4779B3B2B86" xlink:to="loc_ftnt_CoyotePointSystemsInc.Member_EFD4AE958DC568126EADB4779B3B016F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_Goodwill" xlink:label="loc_us-gaap_Goodwill_D09BF111FBA8053116BEB4779B3BB7CA" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D3AA8E3C647C27BB4D4FB4779B3B25D2" xlink:to="loc_us-gaap_Goodwill_D09BF111FBA8053116BEB4779B3BB7CA" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fortinet.com/role/GoodwillAndOtherIntangibleAssetsnetTables" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/IncomeTaxes" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/IncomeTaxesDetails" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/Inventory" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/InventoryDetails" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/InventoryTables" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/NetIncomePerShare" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/NetIncomePerShareAntiDilutiveSecuritiesDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_085579D1A9907C22A82E8E2E9C9CC2A7" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_AC9DAD6B69672AC8F80E8E2E9C9BF326" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_085579D1A9907C22A82E8E2E9C9CC2A7" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_AC9DAD6B69672AC8F80E8E2E9C9BF326" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_62CE23687ABA07F39D698E2E9C9B9910" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_AC9DAD6B69672AC8F80E8E2E9C9BF326" xlink:to="loc_us-gaap_AwardTypeAxis_62CE23687ABA07F39D698E2E9C9B9910" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6661575F5570616B0EA38E2E9C9B49F2_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_62CE23687ABA07F39D698E2E9C9B9910" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6661575F5570616B0EA38E2E9C9B49F2_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6661575F5570616B0EA38E2E9C9B49F2" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_62CE23687ABA07F39D698E2E9C9B9910" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6661575F5570616B0EA38E2E9C9B49F2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="loc_us-gaap_EmployeeStockOptionMember_59B04E35E852B6426A188E2E9C9BD5D8" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6661575F5570616B0EA38E2E9C9B49F2" xlink:to="loc_us-gaap_EmployeeStockOptionMember_59B04E35E852B6426A188E2E9C9BD5D8" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_B8A72FD2C261ECA99EC08E2E9C9BD7A4" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6661575F5570616B0EA38E2E9C9B49F2" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_B8A72FD2C261ECA99EC08E2E9C9BD7A4" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EmployeeStockMember" xlink:label="loc_us-gaap_EmployeeStockMember_DE615AA64DA0A80F90498E2E9C9BAF9A" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6661575F5570616B0EA38E2E9C9B49F2" xlink:to="loc_us-gaap_EmployeeStockMember_DE615AA64DA0A80F90498E2E9C9BAF9A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_1055FDE9AC0EEE20340C8E2E9C9BE376" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_AC9DAD6B69672AC8F80E8E2E9C9BF326" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_1055FDE9AC0EEE20340C8E2E9C9BE376" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_3CBA0310400DD14D23DD8E2E9C9B1910_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_1055FDE9AC0EEE20340C8E2E9C9BE376" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_3CBA0310400DD14D23DD8E2E9C9B1910_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_3CBA0310400DD14D23DD8E2E9C9B1910" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_1055FDE9AC0EEE20340C8E2E9C9BE376" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_3CBA0310400DD14D23DD8E2E9C9B1910" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockCompensationPlanMember" xlink:label="loc_us-gaap_StockCompensationPlanMember_CEEE5BB0298DFFB3878B8E2E9C9CDEAC" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_3CBA0310400DD14D23DD8E2E9C9B1910" xlink:to="loc_us-gaap_StockCompensationPlanMember_CEEE5BB0298DFFB3878B8E2E9C9CDEAC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_C1FD3B7CAF0CC097FF9D8E2E9C9CF9E2" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_085579D1A9907C22A82E8E2E9C9CC2A7" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_C1FD3B7CAF0CC097FF9D8E2E9C9CF9E2" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fortinet.com/role/NetIncomePerShareCalculationOfBasicAndDilutedDetails" xlink:type="extended">
    <loc xlink:href="ftnt-20140331.xsd#ftnt_EarningsPerShareLineItems" xlink:label="loc_ftnt_EarningsPerShareLineItems_AA74734CE4C7929DD98F8E2E9B5F62E1" xlink:type="locator" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_ScheduleOfEarningsPerShareTable" xlink:label="loc_ftnt_ScheduleOfEarningsPerShareTable_D1E4BC87F51758E9A1508E2E9B5EB45E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ftnt_EarningsPerShareLineItems_AA74734CE4C7929DD98F8E2E9B5F62E1" xlink:to="loc_ftnt_ScheduleOfEarningsPerShareTable_D1E4BC87F51758E9A1508E2E9B5EB45E" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_49BEE4B44ADC46F8C2AB8E2E9B5E6FF8" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ftnt_ScheduleOfEarningsPerShareTable_D1E4BC87F51758E9A1508E2E9B5EB45E" xlink:to="loc_us-gaap_AwardTypeAxis_49BEE4B44ADC46F8C2AB8E2E9B5E6FF8" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_A5C35C2D7B0861B6B8E38E2E9B5EA171_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_49BEE4B44ADC46F8C2AB8E2E9B5E6FF8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_A5C35C2D7B0861B6B8E38E2E9B5EA171_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_A5C35C2D7B0861B6B8E38E2E9B5EA171" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_49BEE4B44ADC46F8C2AB8E2E9B5E6FF8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_A5C35C2D7B0861B6B8E38E2E9B5EA171" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="loc_us-gaap_EmployeeStockOptionMember_70A84089380C4B1440408E2E9B5FF1AE" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_A5C35C2D7B0861B6B8E38E2E9B5EA171" xlink:to="loc_us-gaap_EmployeeStockOptionMember_70A84089380C4B1440408E2E9B5FF1AE" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_85CB98F6D377937D638B8E2E9B5FEA5F" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_A5C35C2D7B0861B6B8E38E2E9B5EA171" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_85CB98F6D377937D638B8E2E9B5FEA5F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EmployeeStockMember" xlink:label="loc_us-gaap_EmployeeStockMember_6136FA518C4CDBB1F8468E2E9B5F142D" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_A5C35C2D7B0861B6B8E38E2E9B5EA171" xlink:to="loc_us-gaap_EmployeeStockMember_6136FA518C4CDBB1F8468E2E9B5F142D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="loc_us-gaap_NetIncomeLoss_20C4FF65A9B0C35D2C758E2E9B5FF421" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ftnt_EarningsPerShareLineItems_AA74734CE4C7929DD98F8E2E9B5F62E1" xlink:to="loc_us-gaap_NetIncomeLoss_20C4FF65A9B0C35D2C758E2E9B5FF421" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract_E8D0A5FDDA223848DCB28E2E9B5F7C23" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ftnt_EarningsPerShareLineItems_AA74734CE4C7929DD98F8E2E9B5F62E1" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract_E8D0A5FDDA223848DCB28E2E9B5F7C23" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_DF16490FEF0432645D128E2E9B5F10F9" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract_E8D0A5FDDA223848DCB28E2E9B5F7C23" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_DF16490FEF0432645D128E2E9B5F10F9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_D5F1A29F9B947335438B8E2E9B5F671A" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ftnt_EarningsPerShareLineItems_AA74734CE4C7929DD98F8E2E9B5F62E1" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_D5F1A29F9B947335438B8E2E9B5F671A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract" xlink:label="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_D8DC8C32741F0D70FA068E2E9B5F7D44" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ftnt_EarningsPerShareLineItems_AA74734CE4C7929DD98F8E2E9B5F62E1" xlink:to="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_D8DC8C32741F0D70FA068E2E9B5F7D44" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements" xlink:label="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_00ABC13537BDE88E0CDA8E2E9B5FC626" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_D8DC8C32741F0D70FA068E2E9B5F7D44" xlink:to="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_00ABC13537BDE88E0CDA8E2E9B5FC626" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_858EAD18FCE964C3B1C58E2E9B5F1A8A" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_D8DC8C32741F0D70FA068E2E9B5F7D44" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_858EAD18FCE964C3B1C58E2E9B5F1A8A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EarningsPerShareBasic" xlink:label="loc_us-gaap_EarningsPerShareBasic_12005085EECD08033BFD8E2E9B5F5949" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ftnt_EarningsPerShareLineItems_AA74734CE4C7929DD98F8E2E9B5F62E1" xlink:to="loc_us-gaap_EarningsPerShareBasic_12005085EECD08033BFD8E2E9B5F5949" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EarningsPerShareDiluted" xlink:label="loc_us-gaap_EarningsPerShareDiluted_E11A2F8EB4817F4A40F88E2E9B603111" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ftnt_EarningsPerShareLineItems_AA74734CE4C7929DD98F8E2E9B5F62E1" xlink:to="loc_us-gaap_EarningsPerShareDiluted_E11A2F8EB4817F4A40F88E2E9B603111" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fortinet.com/role/NetIncomePerShareTables" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/PropertyAndEquipmentnet" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/PropertyAndEquipmentnetDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PropertyPlantAndEquipmentLineItems" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_DFE8F51197A759C13989AA204DCBA81A" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_8F32FD3F5F4D2BB12CE8AA204DCBC091" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_DFE8F51197A759C13989AA204DCBA81A" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_8F32FD3F5F4D2BB12CE8AA204DCBC091" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_3A68C36A495F83294025AA204DCB900F" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_8F32FD3F5F4D2BB12CE8AA204DCBC091" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_3A68C36A495F83294025AA204DCB900F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_5BA967F800C4C5D2B70AAA204DCB7EE6_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_3A68C36A495F83294025AA204DCB900F" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_5BA967F800C4C5D2B70AAA204DCB7EE6_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_5BA967F800C4C5D2B70AAA204DCB7EE6" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_3A68C36A495F83294025AA204DCB900F" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_5BA967F800C4C5D2B70AAA204DCB7EE6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LandMember" xlink:label="loc_us-gaap_LandMember_C6717880ED057076C70EAA204DCB1504" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_5BA967F800C4C5D2B70AAA204DCB7EE6" xlink:to="loc_us-gaap_LandMember_C6717880ED057076C70EAA204DCB1504" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BuildingAndBuildingImprovementsMember" xlink:label="loc_us-gaap_BuildingAndBuildingImprovementsMember_1F2CD94E35E7DDF2B9EFAA204DCBE61C" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_5BA967F800C4C5D2B70AAA204DCB7EE6" xlink:to="loc_us-gaap_BuildingAndBuildingImprovementsMember_1F2CD94E35E7DDF2B9EFAA204DCBE61C" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_EvaluationUnitsMember" xlink:label="loc_ftnt_EvaluationUnitsMember_00736AEA047E1C424403AA204DCB28B7" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_5BA967F800C4C5D2B70AAA204DCB7EE6" xlink:to="loc_ftnt_EvaluationUnitsMember_00736AEA047E1C424403AA204DCB28B7" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_ComputerEquipmentSoftwareandToolingMember" xlink:label="loc_ftnt_ComputerEquipmentSoftwareandToolingMember_769C1FC8744D33C59EC5AA22CB172F8B" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_5BA967F800C4C5D2B70AAA204DCB7EE6" xlink:to="loc_ftnt_ComputerEquipmentSoftwareandToolingMember_769C1FC8744D33C59EC5AA22CB172F8B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FurnitureAndFixturesMember" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_9A96F3326FCDF90C2E9FAA204DCBD54D" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_5BA967F800C4C5D2B70AAA204DCB7EE6" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_9A96F3326FCDF90C2E9FAA204DCBD54D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConstructionInProgressMember" xlink:label="loc_us-gaap_ConstructionInProgressMember_8E96E0C3626A30589949AA204DCB92E9" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_5BA967F800C4C5D2B70AAA204DCB7EE6" xlink:to="loc_us-gaap_ConstructionInProgressMember_8E96E0C3626A30589949AA204DCB92E9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LeaseholdsAndLeaseholdImprovementsMember" xlink:label="loc_us-gaap_LeaseholdsAndLeaseholdImprovementsMember_8F6A6BCB98EAE82D3E87AA204DCB35ED" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_5BA967F800C4C5D2B70AAA204DCB7EE6" xlink:to="loc_us-gaap_LeaseholdsAndLeaseholdImprovementsMember_8F6A6BCB98EAE82D3E87AA204DCB35ED" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNetByTypeAbstract" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNetByTypeAbstract_5EEC3E7E74EAE7092846AA204DCB5D18" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_DFE8F51197A759C13989AA204DCBA81A" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNetByTypeAbstract_5EEC3E7E74EAE7092846AA204DCB5D18" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PropertyPlantAndEquipmentGross" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_85C0644D7414D8C81CB8AA204DCB08EC" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentNetByTypeAbstract_5EEC3E7E74EAE7092846AA204DCB5D18" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_85C0644D7414D8C81CB8AA204DCB08EC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_853AE8BA62BEC1F36E36AA204DCB19AC" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentNetByTypeAbstract_5EEC3E7E74EAE7092846AA204DCB5D18" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_853AE8BA62BEC1F36E36AA204DCB19AC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_D703380A587CFE955C3CAA204DCB8CE4" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentNetByTypeAbstract_5EEC3E7E74EAE7092846AA204DCB5D18" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_D703380A587CFE955C3CAA204DCB8CE4" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_Depreciation" xlink:label="loc_us-gaap_Depreciation_B87BB0DCE4243B910054AA204DCB173F" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_DFE8F51197A759C13989AA204DCBA81A" xlink:to="loc_us-gaap_Depreciation_B87BB0DCE4243B910054AA204DCB173F" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fortinet.com/role/PropertyAndEquipmentnetTables" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/SegmentInformation" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/SegmentInformationDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentReportingInformationLineItems" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_DC5881D7120811C2A989AFA8BA7EE602" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_49F0BB3F94E5D9CE10CDAFA8BA7C95DB" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_DC5881D7120811C2A989AFA8BA7EE602" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_49F0BB3F94E5D9CE10CDAFA8BA7C95DB" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorCustomersAxis" xlink:label="loc_us-gaap_MajorCustomersAxis_BD39CE7C33F9A3687972AFB3F7941422" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_49F0BB3F94E5D9CE10CDAFA8BA7C95DB" xlink:to="loc_us-gaap_MajorCustomersAxis_BD39CE7C33F9A3687972AFB3F7941422" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NameOfMajorCustomerDomain" xlink:label="loc_us-gaap_NameOfMajorCustomerDomain_2F773681E2B18C742325AFB85B1181D5_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MajorCustomersAxis_BD39CE7C33F9A3687972AFB3F7941422" xlink:to="loc_us-gaap_NameOfMajorCustomerDomain_2F773681E2B18C742325AFB85B1181D5_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NameOfMajorCustomerDomain" xlink:label="loc_us-gaap_NameOfMajorCustomerDomain_2F773681E2B18C742325AFB85B1181D5" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MajorCustomersAxis_BD39CE7C33F9A3687972AFB3F7941422" xlink:to="loc_us-gaap_NameOfMajorCustomerDomain_2F773681E2B18C742325AFB85B1181D5" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_ExclusiveNetworksGroupMember" xlink:label="loc_ftnt_ExclusiveNetworksGroupMember_446CCBD8F63FCD149E66AFB566D719A9" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NameOfMajorCustomerDomain_2F773681E2B18C742325AFB85B1181D5" xlink:to="loc_ftnt_ExclusiveNetworksGroupMember_446CCBD8F63FCD149E66AFB566D719A9" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_IngramMicroMember" xlink:label="loc_ftnt_IngramMicroMember_0F39B73C43A0B85499B0AFB81236EC10" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NameOfMajorCustomerDomain_2F773681E2B18C742325AFB85B1181D5" xlink:to="loc_ftnt_IngramMicroMember_0F39B73C43A0B85499B0AFB81236EC10" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_10BAB9C8EC6DA2F0B960AFA8BA7C1415" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_49F0BB3F94E5D9CE10CDAFA8BA7C95DB" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_10BAB9C8EC6DA2F0B960AFA8BA7C1415" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_44C27EE48F5B7EAC4026AFA8BA7CB80D_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_10BAB9C8EC6DA2F0B960AFA8BA7C1415" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_44C27EE48F5B7EAC4026AFA8BA7CB80D_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_44C27EE48F5B7EAC4026AFA8BA7CB80D" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_10BAB9C8EC6DA2F0B960AFA8BA7C1415" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_44C27EE48F5B7EAC4026AFA8BA7CB80D" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_SalesRevenueMember" xlink:label="loc_ftnt_SalesRevenueMember_6F530FA93BE3D4BDFA93AFA8BA7C4D08" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_44C27EE48F5B7EAC4026AFA8BA7CB80D" xlink:to="loc_ftnt_SalesRevenueMember_6F530FA93BE3D4BDFA93AFA8BA7C4D08" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConcentrationRiskByTypeAxis" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_4971A2A4229A3D2B06D1AFA8BA7DB80B" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_49F0BB3F94E5D9CE10CDAFA8BA7C95DB" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_4971A2A4229A3D2B06D1AFA8BA7DB80B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConcentrationRiskTypeDomain" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_C08D4785413EBD0A4D16AFA8BA7D4CE4_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_4971A2A4229A3D2B06D1AFA8BA7DB80B" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_C08D4785413EBD0A4D16AFA8BA7D4CE4_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConcentrationRiskTypeDomain" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_C08D4785413EBD0A4D16AFA8BA7D4CE4" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_4971A2A4229A3D2B06D1AFA8BA7DB80B" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_C08D4785413EBD0A4D16AFA8BA7D4CE4" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CustomerConcentrationRiskMember" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_5F86DEA3D21BC1890A13AFA8BA7D0CDC" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_C08D4785413EBD0A4D16AFA8BA7D4CE4" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_5F86DEA3D21BC1890A13AFA8BA7D0CDC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementGeographicalAxis" xlink:label="loc_us-gaap_StatementGeographicalAxis_BB72C357627AE94274E0AFA8BA7D492A" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_49F0BB3F94E5D9CE10CDAFA8BA7C95DB" xlink:to="loc_us-gaap_StatementGeographicalAxis_BB72C357627AE94274E0AFA8BA7D492A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentGeographicalDomain" xlink:label="loc_us-gaap_SegmentGeographicalDomain_690E6EB4F546CE6A22DEAFA8BA7D7405_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementGeographicalAxis_BB72C357627AE94274E0AFA8BA7D492A" xlink:to="loc_us-gaap_SegmentGeographicalDomain_690E6EB4F546CE6A22DEAFA8BA7D7405_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentGeographicalDomain" xlink:label="loc_us-gaap_SegmentGeographicalDomain_690E6EB4F546CE6A22DEAFA8BA7D7405" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementGeographicalAxis_BB72C357627AE94274E0AFA8BA7D492A" xlink:to="loc_us-gaap_SegmentGeographicalDomain_690E6EB4F546CE6A22DEAFA8BA7D7405" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AmericasMember" xlink:label="loc_us-gaap_AmericasMember_3DDCA30196E676BCAC5DAFA8BA7DBB28" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentGeographicalDomain_690E6EB4F546CE6A22DEAFA8BA7D7405" xlink:to="loc_us-gaap_AmericasMember_3DDCA30196E676BCAC5DAFA8BA7DBB28" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/country/2013/country-2013-01-31.xsd#country_US" xlink:label="loc_country_US_CB57CC7F5EB5B906D261AFA8BA7D0F58" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AmericasMember_3DDCA30196E676BCAC5DAFA8BA7DBB28" xlink:to="loc_country_US_CB57CC7F5EB5B906D261AFA8BA7D0F58" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_CanadaMember" xlink:label="loc_ftnt_CanadaMember_AC569EF6A306A8395D2DAFA8BA7D90A5" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AmericasMember_3DDCA30196E676BCAC5DAFA8BA7DBB28" xlink:to="loc_ftnt_CanadaMember_AC569EF6A306A8395D2DAFA8BA7D90A5" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_OtherAmericasMember" xlink:label="loc_ftnt_OtherAmericasMember_D21C367C40CAB84D19FCAFA8BA7DB550" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AmericasMember_3DDCA30196E676BCAC5DAFA8BA7DBB28" xlink:to="loc_ftnt_OtherAmericasMember_D21C367C40CAB84D19FCAFA8BA7DB550" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_EuropeMiddleEastAndAfricaMember" xlink:label="loc_ftnt_EuropeMiddleEastAndAfricaMember_761AC4904B63968FCEB8AFA8BA7D2B66" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentGeographicalDomain_690E6EB4F546CE6A22DEAFA8BA7D7405" xlink:to="loc_ftnt_EuropeMiddleEastAndAfricaMember_761AC4904B63968FCEB8AFA8BA7D2B66" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_AsiaPacificAndJapanMember" xlink:label="loc_ftnt_AsiaPacificAndJapanMember_60F84FFD3E6111330191AFA8BA7E11E2" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentGeographicalDomain_690E6EB4F546CE6A22DEAFA8BA7D7405" xlink:to="loc_ftnt_AsiaPacificAndJapanMember_60F84FFD3E6111330191AFA8BA7E11E2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SalesRevenueNet" xlink:label="loc_us-gaap_SalesRevenueNet_27D5C7D260A8826144A3AFA8BA7E3BE1" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_DC5881D7120811C2A989AFA8BA7EE602" xlink:to="loc_us-gaap_SalesRevenueNet_27D5C7D260A8826144A3AFA8BA7E3BE1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConcentrationRiskPercentage1" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_565952513C5CA62F2066AFA8BA7EEE5A" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_DC5881D7120811C2A989AFA8BA7EE602" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_565952513C5CA62F2066AFA8BA7EEE5A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_BD033F76AB070E483C4EAFA8BA7E54AF" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_DC5881D7120811C2A989AFA8BA7EE602" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_BD033F76AB070E483C4EAFA8BA7E54AF" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fortinet.com/role/SegmentInformationTables" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/StockholdersEquity" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/StockholdersEquityAllocationOfStockBasedCompensationExpenseDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_BBF21F6879537803A18BAEA10CE5BE34" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_63334CD03D93EE5E75AEAEA10CE41467" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_BBF21F6879537803A18BAEA10CE5BE34" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_63334CD03D93EE5E75AEAEA10CE41467" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_2FE8BC0715F11C36AAEDAEA10CE4D3D1" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_63334CD03D93EE5E75AEAEA10CE41467" xlink:to="loc_us-gaap_AwardTypeAxis_2FE8BC0715F11C36AAEDAEA10CE4D3D1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_11551FC053EBA650A20BAEA10CE4C1A8_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_2FE8BC0715F11C36AAEDAEA10CE4D3D1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_11551FC053EBA650A20BAEA10CE4C1A8_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_11551FC053EBA650A20BAEA10CE4C1A8" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_2FE8BC0715F11C36AAEDAEA10CE4D3D1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_11551FC053EBA650A20BAEA10CE4C1A8" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="loc_us-gaap_EmployeeStockOptionMember_4B1A8C175F5421C45CA8AEA10CE44E8D" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_11551FC053EBA650A20BAEA10CE4C1A8" xlink:to="loc_us-gaap_EmployeeStockOptionMember_4B1A8C175F5421C45CA8AEA10CE44E8D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_0E4203AD8127FF91AD1CAEA10CE49A6F" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_11551FC053EBA650A20BAEA10CE4C1A8" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_0E4203AD8127FF91AD1CAEA10CE49A6F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EmployeeStockMember" xlink:label="loc_us-gaap_EmployeeStockMember_1476419C1F56AA628FC0AEA10CE4974D" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_11551FC053EBA650A20BAEA10CE4C1A8" xlink:to="loc_us-gaap_EmployeeStockMember_1476419C1F56AA628FC0AEA10CE4974D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_A0F817481736006FF2B7AEA10CE48E1A" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_63334CD03D93EE5E75AEAEA10CE41467" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_A0F817481736006FF2B7AEA10CE48E1A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_21FC52B5CB56F4F4EF55AEA10CE49B00_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_A0F817481736006FF2B7AEA10CE48E1A" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_21FC52B5CB56F4F4EF55AEA10CE49B00_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_21FC52B5CB56F4F4EF55AEA10CE49B00" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_A0F817481736006FF2B7AEA10CE48E1A" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_21FC52B5CB56F4F4EF55AEA10CE49B00" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_CostOfGoodsSoldMember" xlink:label="loc_ftnt_CostOfGoodsSoldMember_91EEE99A1F4B63323DD0AEA10CE4D2AC" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_21FC52B5CB56F4F4EF55AEA10CE49B00" xlink:to="loc_ftnt_CostOfGoodsSoldMember_91EEE99A1F4B63323DD0AEA10CE4D2AC" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_CostOfServicesMember" xlink:label="loc_ftnt_CostOfServicesMember_1E15C57CE6D1E3382F52AEA10CE4EA2A" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_21FC52B5CB56F4F4EF55AEA10CE49B00" xlink:to="loc_ftnt_CostOfServicesMember_1E15C57CE6D1E3382F52AEA10CE4EA2A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ResearchAndDevelopmentExpenseMember" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpenseMember_7F626A8D45D4C8A0C09AAEA10CE4B793" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_21FC52B5CB56F4F4EF55AEA10CE49B00" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpenseMember_7F626A8D45D4C8A0C09AAEA10CE4B793" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SellingAndMarketingExpenseMember" xlink:label="loc_us-gaap_SellingAndMarketingExpenseMember_5B7065555CA7A1631BCDAEA10CE533B8" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_21FC52B5CB56F4F4EF55AEA10CE49B00" xlink:to="loc_us-gaap_SellingAndMarketingExpenseMember_5B7065555CA7A1631BCDAEA10CE533B8" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_GeneralAndAdministrativeExpenseMember" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_A6CB3CC74B6515D4FF30AEA10CE5E1CA" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_21FC52B5CB56F4F4EF55AEA10CE49B00" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_A6CB3CC74B6515D4FF30AEA10CE5E1CA" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_010A59F2DABE4D88C226AEA10CE514AD" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_BBF21F6879537803A18BAEA10CE5BE34" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_010A59F2DABE4D88C226AEA10CE514AD" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitRealizedFromExerciseOfStockOptions" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitRealizedFromExerciseOfStockOptions_35EB8CF3F9B57D5374A6AEA10CE5F783" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_BBF21F6879537803A18BAEA10CE5BE34" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitRealizedFromExerciseOfStockOptions_35EB8CF3F9B57D5374A6AEA10CE5F783" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fortinet.com/role/StockholdersEquityDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E20498486D9367C20211D30A55AD2FA1" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_B3A9D31BB97EB4921FE1D30A55AD0424" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E20498486D9367C20211D30A55AD2FA1" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_B3A9D31BB97EB4921FE1D30A55AD0424" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_26D945DF4FF86B87EDFDD30A55ADF791" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_B3A9D31BB97EB4921FE1D30A55AD0424" xlink:to="loc_us-gaap_AwardTypeAxis_26D945DF4FF86B87EDFDD30A55ADF791" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_F6845EB56B08D199B5A1D30A55AD7BE9_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_26D945DF4FF86B87EDFDD30A55ADF791" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_F6845EB56B08D199B5A1D30A55AD7BE9_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_F6845EB56B08D199B5A1D30A55AD7BE9" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_26D945DF4FF86B87EDFDD30A55ADF791" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_F6845EB56B08D199B5A1D30A55AD7BE9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="loc_us-gaap_EmployeeStockOptionMember_98F142ADB48D24D6A2ACD30A55AD437A" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_F6845EB56B08D199B5A1D30A55AD7BE9" xlink:to="loc_us-gaap_EmployeeStockOptionMember_98F142ADB48D24D6A2ACD30A55AD437A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract_19E231D111464D67F33ED30A55AD87FE" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E20498486D9367C20211D30A55AD2FA1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract_19E231D111464D67F33ED30A55AD87FE" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_9535A5C94357C5AD48BCD30A55AD4436" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract_19E231D111464D67F33ED30A55AD87FE" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_9535A5C94357C5AD48BCD30A55AD4436" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_883AA20C50C05FE57738D30A55AD0986" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract_19E231D111464D67F33ED30A55AD87FE" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_883AA20C50C05FE57738D30A55AD0986" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_82428EE9DB966E2FF5B0D30A55AD40A1" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract_19E231D111464D67F33ED30A55AD87FE" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_82428EE9DB966E2FF5B0D30A55AD40A1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_86C873A3A827CF496A97D30A55AD4FDA" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract_19E231D111464D67F33ED30A55AD87FE" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_86C873A3A827CF496A97D30A55AD4FDA" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_D7B7821E6C409F25E1E5D30A55AEE89A" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E20498486D9367C20211D30A55AD2FA1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_D7B7821E6C409F25E1E5D30A55AEE89A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_A8C8299ED44BAC8AB48ED30A55AE61FD" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_D7B7821E6C409F25E1E5D30A55AEE89A" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_A8C8299ED44BAC8AB48ED30A55AE61FD" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod_67ECD44CE7A61B074FBCD30A55AE4132" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_D7B7821E6C409F25E1E5D30A55AEE89A" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod_67ECD44CE7A61B074FBCD30A55AE4132" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_30D8845DC6A1F4A0D2C4D30A55AE6B64" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_D7B7821E6C409F25E1E5D30A55AEE89A" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_30D8845DC6A1F4A0D2C4D30A55AE6B64" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_FB6FF53FFD8809007C00D30A55AE8968" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_D7B7821E6C409F25E1E5D30A55AEE89A" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_FB6FF53FFD8809007C00D30A55AE8968" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_4844ADA864D0587F7FE7D30A55AEBB47" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E20498486D9367C20211D30A55AD2FA1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_4844ADA864D0587F7FE7D30A55AEBB47" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_434EEADFD7C212F6CAA9D30A55AE7409" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_4844ADA864D0587F7FE7D30A55AEBB47" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_434EEADFD7C212F6CAA9D30A55AE7409" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_03B4FF8021562516694AD30A55AE4A3D" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_4844ADA864D0587F7FE7D30A55AEBB47" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_03B4FF8021562516694AD30A55AE4A3D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_4096FAC955123BBA721CD30A55AE235A" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_4844ADA864D0587F7FE7D30A55AEBB47" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_4096FAC955123BBA721CD30A55AE235A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_488FAE4CBB0856AA1EDBD30A55AE09DF" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_4844ADA864D0587F7FE7D30A55AEBB47" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_488FAE4CBB0856AA1EDBD30A55AE09DF" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_EEB684084EE213D4EB46D30A55AE2BBA" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E20498486D9367C20211D30A55AD2FA1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_EEB684084EE213D4EB46D30A55AE2BBA" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber_F016CF71FCD02C557BACD30A55AE084E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_EEB684084EE213D4EB46D30A55AE2BBA" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber_F016CF71FCD02C557BACD30A55AE084E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice_C5B4D0EC1B29DA8E597CD30A55AE3788" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_EEB684084EE213D4EB46D30A55AE2BBA" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice_C5B4D0EC1B29DA8E597CD30A55AE3788" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1_39E6D1AC855FB02294AFD30A55AFB3EC" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_EEB684084EE213D4EB46D30A55AE2BBA" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1_39E6D1AC855FB02294AFD30A55AFB3EC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue_0EE014CB5AB5C3D9D061D30A55AFC65F" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_EEB684084EE213D4EB46D30A55AE2BBA" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue_0EE014CB5AB5C3D9D061D30A55AFC65F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_932A3B37A51C2D9165E5D30A55AF8721" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_EEB684084EE213D4EB46D30A55AE2BBA" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_932A3B37A51C2D9165E5D30A55AF8721" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_6DC6D6B3F0FE84B6CEF1D30A55AF88A7" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_EEB684084EE213D4EB46D30A55AE2BBA" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_6DC6D6B3F0FE84B6CEF1D30A55AF88A7" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1_281B1261B746BF24EA91D30A55AFC3AC" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_EEB684084EE213D4EB46D30A55AE2BBA" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1_281B1261B746BF24EA91D30A55AFC3AC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1_C8F2DC6A44A57665B4CFD30A55AF3D6F" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_EEB684084EE213D4EB46D30A55AE2BBA" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1_C8F2DC6A44A57665B4CFD30A55AF3D6F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_8D5A9865A6830983FA9FD30A55AF6F88" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E20498486D9367C20211D30A55AD2FA1" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_8D5A9865A6830983FA9FD30A55AF6F88" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_4F707294B9684956243FD30A55AF6575" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E20498486D9367C20211D30A55AD2FA1" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_4F707294B9684956243FD30A55AF6575" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_53BA1D7808A7AE35EAF3D30A55AF10EB" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E20498486D9367C20211D30A55AD2FA1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_53BA1D7808A7AE35EAF3D30A55AF10EB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_A311215885D53270818DD30A55AFA07D" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E20498486D9367C20211D30A55AD2FA1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_A311215885D53270818DD30A55AFA07D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1_0A60E38FA1135FB60DCDD30A55AF128F" xlink:type="locator" />
    <definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E20498486D9367C20211D30A55AD2FA1" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1_0A60E38FA1135FB60DCDD30A55AF128F" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fortinet.com/role/StockholdersEquityEsppInformationDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_868103C35FC2B5239E54AFA8BB079CE8" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_16D51348ED593CE2D94DAFA8BB07CC5C" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_868103C35FC2B5239E54AFA8BB079CE8" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_16D51348ED593CE2D94DAFA8BB07CC5C" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_69E346C20B201DE12C17AFA8BB073466" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_16D51348ED593CE2D94DAFA8BB07CC5C" xlink:to="loc_us-gaap_AwardTypeAxis_69E346C20B201DE12C17AFA8BB073466" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_049B0564CE3EB3929B2BAFA8BB073F13_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_69E346C20B201DE12C17AFA8BB073466" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_049B0564CE3EB3929B2BAFA8BB073F13_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_049B0564CE3EB3929B2BAFA8BB073F13" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_69E346C20B201DE12C17AFA8BB073466" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_049B0564CE3EB3929B2BAFA8BB073F13" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_EmployeeStockPurchasePlanMember" xlink:label="loc_ftnt_EmployeeStockPurchasePlanMember_B5C930C3B5066F914A26AFA8BB072F3A" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_049B0564CE3EB3929B2BAFA8BB073F13" xlink:to="loc_ftnt_EmployeeStockPurchasePlanMember_B5C930C3B5066F914A26AFA8BB072F3A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_1B3A719C186050BBA622AFA8BB07B8A2" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_868103C35FC2B5239E54AFA8BB079CE8" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_1B3A719C186050BBA622AFA8BB07B8A2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_45C38D55A78C87BCE579AFA8BB078079" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_868103C35FC2B5239E54AFA8BB079CE8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_45C38D55A78C87BCE579AFA8BB078079" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_EB6F25759A049184124FAFA8BB078AD8" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_868103C35FC2B5239E54AFA8BB079CE8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_EB6F25759A049184124FAFA8BB078AD8" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_BC06AFAFAF31BAF0A82FAFA8BB078765" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_868103C35FC2B5239E54AFA8BB079CE8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_BC06AFAFAF31BAF0A82FAFA8BB078765" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_B08C443D672F091A80B3AFA8BB079308" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_868103C35FC2B5239E54AFA8BB079CE8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_B08C443D672F091A80B3AFA8BB079308" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_3E6AE300E78EE60E6000AFA8BB0710A8" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_868103C35FC2B5239E54AFA8BB079CE8" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_3E6AE300E78EE60E6000AFA8BB0710A8" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsIssuedWeightedAveragePricePerShare" xlink:label="loc_ftnt_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsIssuedWeightedAveragePricePerShare_F99F0BE0333FC6BCA8B2AFA8BB08906D" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_868103C35FC2B5239E54AFA8BB079CE8" xlink:to="loc_ftnt_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsIssuedWeightedAveragePricePerShare_F99F0BE0333FC6BCA8B2AFA8BB08906D" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fortinet.com/role/StockholdersEquityRestrictedStockUnitsActivityDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_B2FDB073982DAEBD3211AEA10BFA11DD" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_1CA4A7652B873A79B403AEA10BFA86AD" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_B2FDB073982DAEBD3211AEA10BFA11DD" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_1CA4A7652B873A79B403AEA10BFA86AD" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_6285F952EBB0FD66D272AEA10BFA9D4B" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_1CA4A7652B873A79B403AEA10BFA86AD" xlink:to="loc_us-gaap_AwardTypeAxis_6285F952EBB0FD66D272AEA10BFA9D4B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_B4AE19E845B468957CA6AEA10BFA471C_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_6285F952EBB0FD66D272AEA10BFA9D4B" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_B4AE19E845B468957CA6AEA10BFA471C_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_B4AE19E845B468957CA6AEA10BFA471C" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_6285F952EBB0FD66D272AEA10BFA9D4B" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_B4AE19E845B468957CA6AEA10BFA471C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_0EA7C08C32DC502CC3C1AEA10BFA1911" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_B4AE19E845B468957CA6AEA10BFA471C" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_0EA7C08C32DC502CC3C1AEA10BFA1911" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_113DDBE6ECC30417A886AEA10BFA91D8" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_B2FDB073982DAEBD3211AEA10BFA11DD" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_113DDBE6ECC30417A886AEA10BFA91D8" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_4FE7B5675B74D98038E3AEA10C0009F9" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_113DDBE6ECC30417A886AEA10BFA91D8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_4FE7B5675B74D98038E3AEA10C0009F9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_C57F01EDD7DB89410406AEA10C004B91" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_113DDBE6ECC30417A886AEA10BFA91D8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_C57F01EDD7DB89410406AEA10C004B91" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_A9F0F0FEE670F49CF23FAEA10C008931" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_113DDBE6ECC30417A886AEA10BFA91D8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_A9F0F0FEE670F49CF23FAEA10C008931" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_B39D77E896A34CB115D7AEA10C0092E8" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_113DDBE6ECC30417A886AEA10BFA91D8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_B39D77E896A34CB115D7AEA10C0092E8" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExpectedToVest" xlink:label="loc_ftnt_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExpectedToVest_5D8F2AEA176CABA6EEC1AEA10C00E4A1" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_B2FDB073982DAEBD3211AEA10BFA11DD" xlink:to="loc_ftnt_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExpectedToVest_5D8F2AEA176CABA6EEC1AEA10C00E4A1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_3BA044140B862F82CEDAAEA10C00F479" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_B2FDB073982DAEBD3211AEA10BFA11DD" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_3BA044140B862F82CEDAAEA10C00F479" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_16BC0E7B2934A5446ADAAEA10C00889C" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_3BA044140B862F82CEDAAEA10C00F479" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_16BC0E7B2934A5446ADAAEA10C00889C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_90D2D73010851A681101AEA10C000682" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_3BA044140B862F82CEDAAEA10C00F479" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_90D2D73010851A681101AEA10C000682" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_22BEDD5ED8B65FAD57D8AEA10C0087EC" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_3BA044140B862F82CEDAAEA10C00F479" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_22BEDD5ED8B65FAD57D8AEA10C0087EC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_E12D026EA0841CDD612FAEA10C0200C7" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_3BA044140B862F82CEDAAEA10C00F479" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_E12D026EA0841CDD612FAEA10C0200C7" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExpectedToVestWeightedAverageGrantDateFairValue" xlink:label="loc_ftnt_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExpectedToVestWeightedAverageGrantDateFairValue_D5A952ADACE651ACB132AEA10C02B57E" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_B2FDB073982DAEBD3211AEA10BFA11DD" xlink:to="loc_ftnt_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExpectedToVestWeightedAverageGrantDateFairValue_D5A952ADACE651ACB132AEA10C02B57E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_B29FA47944C578A0B2DBAEA10C028B02" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_B2FDB073982DAEBD3211AEA10BFA11DD" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_B29FA47944C578A0B2DBAEA10C028B02" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_A8E85C79922AB7FF5A0EAEA10C029E01" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_B2FDB073982DAEBD3211AEA10BFA11DD" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_A8E85C79922AB7FF5A0EAEA10C029E01" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation" xlink:label="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_533688D927126F72F85FAEA10C024C98" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_B2FDB073982DAEBD3211AEA10BFA11DD" xlink:to="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_533688D927126F72F85FAEA10C024C98" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation" xlink:label="loc_us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation_75FF68DA42FE4F7DE28AAEA10C0259BD" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_B2FDB073982DAEBD3211AEA10BFA11DD" xlink:to="loc_us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation_75FF68DA42FE4F7DE28AAEA10C0259BD" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fortinet.com/role/StockholdersEquityShareRepurchaseProgramDetails" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/StockholdersEquityTables" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/SummaryOfSignificantAccountingPolicies" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/SummaryOfSignificantAccountingPoliciesPolicies" xlink:type="extended" />
  <definitionLink xlink:role="http://www.fortinet.com/role/SummaryOfSignificantAccountingPoliciesPropertyAndEquipmentDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PropertyPlantAndEquipmentLineItems" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_5CDCCE54ABBF06D02315AFA8BC5D8422" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_FA5E4BFE69FFE6F745E1AFA8BC5C91AE" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_5CDCCE54ABBF06D02315AFA8BC5D8422" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_FA5E4BFE69FFE6F745E1AFA8BC5C91AE" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_09D6633137127CC62306AFA8BC5C9784" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_FA5E4BFE69FFE6F745E1AFA8BC5C91AE" xlink:to="loc_us-gaap_RangeAxis_09D6633137127CC62306AFA8BC5C9784" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_EBEDCD308DF896EC8A7FAFA8BC5CCDFA_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_09D6633137127CC62306AFA8BC5C9784" xlink:to="loc_us-gaap_RangeMember_EBEDCD308DF896EC8A7FAFA8BC5CCDFA_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_EBEDCD308DF896EC8A7FAFA8BC5CCDFA" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_09D6633137127CC62306AFA8BC5C9784" xlink:to="loc_us-gaap_RangeMember_EBEDCD308DF896EC8A7FAFA8BC5CCDFA" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember_FEF75FB0173A71A0AEE4AFA8BC5C1C40" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_EBEDCD308DF896EC8A7FAFA8BC5CCDFA" xlink:to="loc_us-gaap_MinimumMember_FEF75FB0173A71A0AEE4AFA8BC5C1C40" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember_CBEC1B75EFDD0B7AF568AFA8BC5C88F4" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_EBEDCD308DF896EC8A7FAFA8BC5CCDFA" xlink:to="loc_us-gaap_MaximumMember_CBEC1B75EFDD0B7AF568AFA8BC5C88F4" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_160723525A760413F1C2AFA8BC5CC6BD" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_FA5E4BFE69FFE6F745E1AFA8BC5C91AE" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_160723525A760413F1C2AFA8BC5CC6BD" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_2B3C1C957CEE909EDBDAAFA8BC5C190E_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_160723525A760413F1C2AFA8BC5CC6BD" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_2B3C1C957CEE909EDBDAAFA8BC5C190E_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_2B3C1C957CEE909EDBDAAFA8BC5C190E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_160723525A760413F1C2AFA8BC5CC6BD" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_2B3C1C957CEE909EDBDAAFA8BC5C190E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BuildingAndBuildingImprovementsMember" xlink:label="loc_us-gaap_BuildingAndBuildingImprovementsMember_EB45F786EC7B887EF8EDAFA8BC5CC65B" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_2B3C1C957CEE909EDBDAAFA8BC5C190E" xlink:to="loc_us-gaap_BuildingAndBuildingImprovementsMember_EB45F786EC7B887EF8EDAFA8BC5CC65B" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_EvaluationUnitsMember" xlink:label="loc_ftnt_EvaluationUnitsMember_99B986888A805F09A3FDAFA8BC5D5C01" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_2B3C1C957CEE909EDBDAAFA8BC5C190E" xlink:to="loc_ftnt_EvaluationUnitsMember_99B986888A805F09A3FDAFA8BC5D5C01" xlink:type="arc" />
    <loc xlink:href="ftnt-20140331.xsd#ftnt_ComputerEquipmentSoftwareandToolingMember" xlink:label="loc_ftnt_ComputerEquipmentSoftwareandToolingMember_B7A5CD6A6CE4872CF79FAFA8BC5D76F7" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_2B3C1C957CEE909EDBDAAFA8BC5C190E" xlink:to="loc_ftnt_ComputerEquipmentSoftwareandToolingMember_B7A5CD6A6CE4872CF79FAFA8BC5D76F7" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FurnitureAndFixturesMember" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_0C4B00C04DE0E2B3E658AFA8BC5D056E" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_2B3C1C957CEE909EDBDAAFA8BC5C190E" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_0C4B00C04DE0E2B3E658AFA8BC5D056E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_C3F1A45B82A7C824285AAFA8BC5D5D90" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_5CDCCE54ABBF06D02315AFA8BC5D8422" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_C3F1A45B82A7C824285AAFA8BC5D5D90" xlink:type="arc" />
  </definitionLink>
</linkbase>
