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  <xsd:element abstract="true" id="biib_ELOCTATEMember" name="ELOCTATEMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_EachAdditionalOneBillionUpToTwentyBillionMember" name="EachAdditionalOneBillionUpToTwentyBillionMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_EarningsPerShareTextualAbstract" name="EarningsPerShareTextualAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_EffectiveIncomeTaxRateReconciliationContingentConsideration" name="EffectiveIncomeTaxRateReconciliationContingentConsideration" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_EffectiveIncomeTaxRateReconciliationManufacturingDeduction" name="EffectiveIncomeTaxRateReconciliationManufacturingDeduction" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_EightbillionMember" name="EightbillionMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_EisaiMember" name="EisaiMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_ElevenbillionMember" name="ElevenbillionMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_EmployeeBenefitPlansTextualAbstract" name="EmployeeBenefitPlansTextualAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_EmployeeServiceSharebasedCompensationSharesUsedtoSettleAwards" name="EmployeeServiceSharebasedCompensationSharesUsedtoSettleAwards" nillable="true" substitutionGroup="xbrli:item" type="xbrli:sharesItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_EmployeeStockPurchasePlanMember" name="EmployeeStockPurchasePlanMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_EntityWidePercentageOfRevenueFromMajorDistributors" name="EntityWidePercentageOfRevenueFromMajorDistributors" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_EquityMethodInvestmentOwnershipPercentageMaximum" name="EquityMethodInvestmentOwnershipPercentageMaximum" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_EquityMethodInvestmentsExpectedProfitShare" name="EquityMethodInvestmentsExpectedProfitShare" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_EquityTextualAbstract" name="EquityTextualAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_EstimatedAdditionalPaymentsUponAchievementOfDevelopmentAndCommercialMilestones" name="EstimatedAdditionalPaymentsUponAchievementOfDevelopmentAndCommercialMilestones" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="biib_EstimatedTaxLiabilityOnUndistributedEarningsOfForeignSubsidiaries" name="EstimatedTaxLiabilityOnUndistributedEarningsOfForeignSubsidiaries" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="biib_EstimatedUsefulLivesOfLeaseholdImprovements" name="EstimatedUsefulLivesOfLeaseholdImprovements" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_ExpectedAdditionalMilestonePaymentsOnSuccessfulAchievementOfRegulatoryAndCommercialSalesMilestones" name="ExpectedAdditionalMilestonePaymentsOnSuccessfulAchievementOfRegulatoryAndCommercialSalesMilestones" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="biib_ExpectedAdditionalMilestonePaymentsWhenMeetingCertainSalesThreshold" name="ExpectedAdditionalMilestonePaymentsWhenMeetingCertainSalesThreshold" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="biib_ExpectedLicenseFeeAndRegulatoryMilestonePayments" name="ExpectedLicenseFeeAndRegulatoryMilestonePayments" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="biib_ExpenseIncurredByCollaboration" name="ExpenseIncurredByCollaboration" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="biib_ExpenseReflectedWithinStatementsOfIncome" name="ExpenseReflectedWithinStatementsOfIncome" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_FAMPYRAMember" name="FAMPYRAMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_FLIXABIMember" name="FLIXABIMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_FUMADERMMember" name="FUMADERMMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_FacilityLocationAxis" name="FacilityLocationAxis" nillable="true" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_FacilityLocationDomain" name="FacilityLocationDomain" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_FinancialInstrumentsTextualAbstract" name="FinancialInstrumentsTextualAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_ForeignSalesRequiredToTriggerMilestone" name="ForeignSalesRequiredToTriggerMilestone" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_FumapharmAgMember" name="FumapharmAgMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_FutureContingentMilestoneTypesAxis" name="FutureContingentMilestoneTypesAxis" nillable="true" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_FutureContingentMilestoneTypesDomain" name="FutureContingentMilestoneTypesDomain" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_FutureContingentPaymentForAnnualWorldwideNetSalesThatExceed20Billion" name="FutureContingentPaymentForAnnualWorldwideNetSalesThatExceed20Billion" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="biib_FutureContingentPaymentForAnnualWorldwideNetSalesUpTo20Billion" name="FutureContingentPaymentForAnnualWorldwideNetSalesUpTo20Billion" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="biib_FutureContingentPaymentThreshold" name="FutureContingentPaymentThreshold" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="biib_FutureRoyaltiesPercentageToBeReceivedOnSaleOfProduct" name="FutureRoyaltiesPercentageToBeReceivedOnSaleOfProduct" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_Futurepercentageofcopromotionoperatingprofits" name="Futurepercentageofcopromotionoperatingprofits" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_Futureresearchanddevelopmentcommitment" name="Futureresearchanddevelopmentcommitment" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="biib_GAZYVAMember" name="GAZYVAMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_GainOnSaleOfRights" name="GainOnSaleOfRights" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_GovernmentSecuritiesCurrentMember" name="GovernmentSecuritiesCurrentMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_GovernmentSecuritiesNonCurrentMember" name="GovernmentSecuritiesNonCurrentMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_InLicensedPatentsMember" name="InLicensedPatentsMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_IncomeTaxesTextualAbstract" name="IncomeTaxesTextualAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_IncreasedCarryingAmountOfSeniorNotes" name="IncreasedCarryingAmountOfSeniorNotes" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="biib_IndefiniteLivedIntangibleAssetsUsefulLife" name="IndefiniteLivedIntangibleAssetsUsefulLife" nillable="true" substitutionGroup="xbrli:item" type="us-types:durationStringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_IntangibleAssetsAndGoodwillAdditionalTextualAbstract" name="IntangibleAssetsAndGoodwillAdditionalTextualAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_IntangibleAssetsExcludingGoodwillTableTextBlock" name="IntangibleAssetsExcludingGoodwillTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_InterestInSubsidiary" name="InterestInSubsidiary" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_Inventorynetcurrentandnoncurrent" name="Inventorynetcurrentandnoncurrent" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="biib_InvestmentInBiotechnologyCompaniesThatAreDeterminedToBeUnconsolidatedVariableInterestEntities" name="InvestmentInBiotechnologyCompaniesThatAreDeterminedToBeUnconsolidatedVariableInterestEntities" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="biib_InvestmentInVariableInterestEntitiesTextualAbstract" name="InvestmentInVariableInterestEntitiesTextualAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_InvestmentsByThirdPartyInJointVentureAsPerAgreement" name="InvestmentsByThirdPartyInJointVentureAsPerAgreement" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
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  <xsd:element abstract="true" id="biib_IonisPharmaceuticalsInc.Member" name="IonisPharmaceuticalsInc.Member" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_IonisPharmaceuticalsMember" name="IonisPharmaceuticalsMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_JointVentureOwnerShipPercentageByThirdParty" name="JointVentureOwnerShipPercentageByThirdParty" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_LeadprogramsMember" name="LeadprogramsMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_LiabilityForFairValueOfOptionsGrantedUnderAgreement" name="LiabilityForFairValueOfOptionsGrantedUnderAgreement" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="biib_LicenseFee" name="LicenseFee" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="biib_LossContingencyAdjustmentRelatedToClaimAmountPercent" name="LossContingencyAdjustmentRelatedToClaimAmountPercent" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="biib_MajorDistributorAxis" name="MajorDistributorAxis" nillable="true" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_MajorDistributorDomain" name="MajorDistributorDomain" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_MarketStockUnitsActivityAbstract" name="MarketStockUnitsActivityAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_MarketStockUnitsMember" name="MarketStockUnitsMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_MarketableEquitySecuritiesMember" name="MarketableEquitySecuritiesMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_MaximumTargetNumberOfMarketStockUnitsGrantedBasedOnStockPerformanceInPercent" name="MaximumTargetNumberOfMarketStockUnitsGrantedBasedOnStockPerformanceInPercent" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_MilestonePaymentsMadeDuringPeriod" name="MilestonePaymentsMadeDuringPeriod" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="biib_MinimumQualifyingAgeForEmployeeBenefitPlan" name="MinimumQualifyingAgeForEmployeeBenefitPlan" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_MinimumRentalCommitmentsUnderNoncancellableLeasesAbstract" name="MinimumRentalCommitmentsUnderNoncancellableLeasesAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_MinimumTargetNumberOfMarketStockUnitsGrantedBasedOnStockPerformanceInPercent" name="MinimumTargetNumberOfMarketStockUnitsGrantedBasedOnStockPerformanceInPercent" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_MitsubishiTanabePharmaCorporationMember" name="MitsubishiTanabePharmaCorporationMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_MortgageAndOtherAssetBackedSecuritiesCurrentMember" name="MortgageAndOtherAssetBackedSecuritiesCurrentMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_MortgageAndOtherAssetBackedSecuritiesNonCurrentMember" name="MortgageAndOtherAssetBackedSecuritiesNonCurrentMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_NetMinimumLeasePayments" name="NetMinimumLeasePayments" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="biib_NetMinimumLeasePaymentsThereafter" name="NetMinimumLeasePaymentsThereafter" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="biib_NetMinimumLeasePaymentsWithInFiveYear" name="NetMinimumLeasePaymentsWithInFiveYear" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="biib_NetMinimumLeasePaymentsWithInFourYear" name="NetMinimumLeasePaymentsWithInFourYear" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="biib_NetMinimumLeasePaymentsWithInOneYear" name="NetMinimumLeasePaymentsWithInOneYear" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="biib_NetMinimumLeasePaymentsWithInThreeYear" name="NetMinimumLeasePaymentsWithInThreeYear" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="biib_NetMinimumLeasePaymentsWithInTwoYear" name="NetMinimumLeasePaymentsWithInTwoYear" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="biib_NeurimmuneMember" name="NeurimmuneMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_NeuropathicpainindicationsMember" name="NeuropathicpainindicationsMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_NewAntiCd20Member" name="NewAntiCd20Member" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_NinebillionMember" name="NinebillionMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_Noncontrollinginterestincreasedecreaseother" name="Noncontrollinginterestincreasedecreaseother" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_NotesPayableToFumedicaMember" name="NotesPayableToFumedicaMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_NumberOfDaysForCalculationOfAverageClosingStockPrice" name="NumberOfDaysForCalculationOfAverageClosingStockPrice" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_NumberOfEqualAnnualIncrements" name="NumberOfEqualAnnualIncrements" nillable="true" substitutionGroup="xbrli:item" type="xbrli:integerItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_NumberOfShareBasedCompensationPlansPursuantToWhichAwardsAreCurrentlyBeingMade" name="NumberOfShareBasedCompensationPlansPursuantToWhichAwardsAreCurrentlyBeingMade" nillable="true" substitutionGroup="xbrli:item" type="xbrli:integerItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_NumberOfSharesOfCommonStockForIssuance" name="NumberOfSharesOfCommonStockForIssuance" nillable="true" substitutionGroup="xbrli:item" type="xbrli:sharesItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_NumeratorAbstract" name="NumeratorAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_OcrelizumabMember" name="OcrelizumabMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_OmnibusPlansMember" name="OmnibusPlansMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_OneBillionMember" name="OneBillionMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_OtherIncomeExpenseNet" name="OtherIncomeExpenseNet" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_OtherresearchanddiscoveryMember" name="OtherresearchanddiscoveryMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_OutLicensedPatentsMember" name="OutLicensedPatentsMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_Overnightreverserepurchaseagreementspercentoftotalassets" name="Overnightreverserepurchaseagreementspercentoftotalassets" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="biib_PLEGRIDYMember" name="PLEGRIDYMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_ParValueOfNotesPayable" name="ParValueOfNotesPayable" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="biib_PaymentTermsOfAccountsReceivable" name="PaymentTermsOfAccountsReceivable" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_PaymentsReturnsAppliedAgainstProductRevenueReservesRelatingToCurrentYear" name="PaymentsReturnsAppliedAgainstProductRevenueReservesRelatingToCurrentYear" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="biib_PaymentsReturnsAppliedAgainstProductRevenueReservesRelatingToPriorYear" name="PaymentsReturnsAppliedAgainstProductRevenueReservesRelatingToPriorYear" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="biib_PercentageOfCoPromotionOperatingLosses" name="PercentageOfCoPromotionOperatingLosses" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_PercentageOfCoPromotionOperatingProfitsFirstFiftyMillion" name="PercentageOfCoPromotionOperatingProfitsFirstFiftyMillion" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="biib_PercentageOfCoPromotionOperatingProfitsGreaterThanFirstFiftyMillion" name="PercentageOfCoPromotionOperatingProfitsGreaterThanFirstFiftyMillion" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="biib_PercentageOfCoPromotionOperatingProfitsGreaterThanFirstFiftyMillionOptionOne" name="PercentageOfCoPromotionOperatingProfitsGreaterThanFirstFiftyMillionOptionOne" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="biib_PercentageOfCoPromotionOperatingProfitsGreaterThanFirstFiftyMillionOptionTwoAbstract" name="PercentageOfCoPromotionOperatingProfitsGreaterThanFirstFiftyMillionOptionTwoAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_PercentageOfCoPromotionOperatingProfitsGreaterThanFirstFiftyMillionOptionTwoSubOptionOne" name="PercentageOfCoPromotionOperatingProfitsGreaterThanFirstFiftyMillionOptionTwoSubOptionOne" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="biib_PercentageOfCoPromotionOperatingProfitsGreaterThanFirstFiftyMillionOptionTwoSubOptionThree" name="PercentageOfCoPromotionOperatingProfitsGreaterThanFirstFiftyMillionOptionTwoSubOptionThree" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="biib_PercentageOfCoPromotionOperatingProfitsGreaterThanFirstFiftyMillionOptionTwoSubOptionTwo" name="PercentageOfCoPromotionOperatingProfitsGreaterThanFirstFiftyMillionOptionTwoSubOptionTwo" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="biib_PercentageOfMarketValuePerShareOfCommonStock" name="PercentageOfMarketValuePerShareOfCommonStock" nillable="true" substitutionGroup="xbrli:item" type="num:perShareItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_PercentageOfMinimumInvestmentReturn" name="PercentageOfMinimumInvestmentReturn" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_PercentageParValueOfSeniorNotes" name="PercentageParValueOfSeniorNotes" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="biib_PercentageReceivablesOfWholesaleDistributorAccountedInConsolidatedReceivables" name="PercentageReceivablesOfWholesaleDistributorAccountedInConsolidatedReceivables" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="biib_PerformanceUnitsMember" name="PerformanceUnitsMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_PerformanceunitsactivityTableTextBlock" name="PerformanceunitsactivityTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_PeriodOfCollaborationAgreement" name="PeriodOfCollaborationAgreement" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_PlanAssetsForDeferredCompensationFairValueDisclosure" name="PlanAssetsForDeferredCompensationFairValueDisclosure" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="biib_PotentialFutureMilestonePaymentsCommitmentToThirdPartyApproximately" name="PotentialFutureMilestonePaymentsCommitmentToThirdPartyApproximately" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="biib_Preapprovalinventory" name="Preapprovalinventory" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="biib_Premiumonequityinvestment" name="Premiumonequityinvestment" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="biib_PretaxProfitSharingFormulaTableTextBlock" name="PretaxProfitSharingFormulaTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_ProceedsFromMarketableDebtSecuritiesAbstract" name="ProceedsFromMarketableDebtSecuritiesAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_PurchasePriceOfCommonStockUnderEspp" name="PurchasePriceOfCommonStockUnderEspp" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_Purchaseofcommonstock" name="Purchaseofcommonstock" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="biib_RateDuringReimbursementPeriod" name="RateDuringReimbursementPeriod" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_RatioOfNumberOfSharesReservedUnderPlan" name="RatioOfNumberOfSharesReservedUnderPlan" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_Reductioninroyaltyrate" name="Reductioninroyaltyrate" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_RegulatoryMilestonesMember" name="RegulatoryMilestonesMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_ReimbursementCostAchievingPeriod" name="ReimbursementCostAchievingPeriod" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_ReimbursementLimitStatedInResolution" name="ReimbursementLimitStatedInResolution" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_ReimbursementUnderAmendedAgreementAmountsPayableAbstract" name="ReimbursementUnderAmendedAgreementAmountsPayableAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_ReimbursementUnderAmendedAgreementAmountsPayableTableTextBlock" name="ReimbursementUnderAmendedAgreementAmountsPayableTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_ReimbursementUnderAmendedAgreementMethod" name="ReimbursementUnderAmendedAgreementMethod" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_RemainingPotentialDevelopmentMilestonePaymentsAndRoyaltiesOnCommercialSalesUnderTermsOfCollaborationAgreement" name="RemainingPotentialDevelopmentMilestonePaymentsAndRoyaltiesOnCommercialSalesUnderTermsOfCollaborationAgreement" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="biib_ResearchAndDevelopmentCostInSupportOfCollaborationAgreement" name="ResearchAndDevelopmentCostInSupportOfCollaborationAgreement" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_Researchanddevelopmentservices" name="Researchanddevelopmentservices" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_ReservesForDiscountsAndAllowancesAbstract" name="ReservesForDiscountsAndAllowancesAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_RestOfWorldMember" name="RestOfWorldMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_RestrictedStockUnitsActivityAbstract" name="RestrictedStockUnitsActivityAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_RestructuringandRelatedCostExpectedCashPayments" name="RestructuringandRelatedCostExpectedCashPayments" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="biib_Restructuringandrelatedcostexpectedpercentageofpositionseliminated" name="Restructuringandrelatedcostexpectedpercentageofpositionseliminated" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_RevenuesFromUnconsolidatedJointBusinessAbstract" name="RevenuesFromUnconsolidatedJointBusinessAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_RevenuesFromUnconsolidatedJointBusinessTableTextBlock" name="RevenuesFromUnconsolidatedJointBusinessTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_RevenuesInPercentageFromAntiCD20TherapeuticPrograms" name="RevenuesInPercentageFromAntiCD20TherapeuticPrograms" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_RevenuesfromantiCD20therapeuticprograms" name="RevenuesfromantiCD20therapeuticprograms" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_RituxanMember" name="RituxanMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_RocheGroupGenentechMember" name="RocheGroupGenentechMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_RodinTherapeuticsMember" name="RodinTherapeuticsMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_RoyaltyAndNetRevenueShareRatesByTerritoryAxis" name="RoyaltyAndNetRevenueShareRatesByTerritoryAxis" nillable="true" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_RoyaltyAndNetRevenueShareRatesByTerritoryDomain" name="RoyaltyAndNetRevenueShareRatesByTerritoryDomain" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_RoyaltyCostofSalesPolicyTextBlock" name="RoyaltyCostofSalesPolicyTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SOD1Member" name="SOD1Member" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SPINRAZAMember" name="SPINRAZAMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_SalesTriggerGrossSalesThreshold" name="SalesTriggerGrossSalesThreshold" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SamsungBiosimilarAgreementMember" name="SamsungBiosimilarAgreementMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SangamoBioSciencesMember" name="SangamoBioSciencesMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_ScheduleOfCashSettledPerformanceSharesActivityTableTextBlock" name="ScheduleOfCashSettledPerformanceSharesActivityTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_ScheduleOfDevelopmentMilestoneAndCollaborationLineItems" name="ScheduleOfDevelopmentMilestoneAndCollaborationLineItems" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_ScheduleOfDevelopmentMilestoneAndCollaborationTable" name="ScheduleOfDevelopmentMilestoneAndCollaborationTable" nillable="true" substitutionGroup="xbrldt:hypercubeItem" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_ScheduleOfMarketStockUnitsActivityTableTextBlock" name="ScheduleOfMarketStockUnitsActivityTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_ScheduleOfPropertyPlantAndEquipmentUsefulLivesTableTextBlock" name="ScheduleOfPropertyPlantAndEquipmentUsefulLivesTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SegmentGeographicalGroupsOfCountriesGroupOtherMember" name="SegmentGeographicalGroupsOfCountriesGroupOtherMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SegmentInformationTextualAbstract" name="SegmentInformationTextualAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SeniorNotesFivePointTwoPercentDueTwentyFortyFiveMember" name="SeniorNotesFivePointTwoPercentDueTwentyFortyFiveMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SeniorNotesFourPointZeroFivePercentDueTwentyTwentyFiveMember" name="SeniorNotesFourPointZeroFivePercentDueTwentyTwentyFiveMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SeniorNotesSixPointEightSevenFivePercentDueTwentyEighteenMember" name="SeniorNotesSixPointEightSevenFivePercentDueTwentyEighteenMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SeniorNotesThreePointSixTwoFivePercentDueTwentyTwentyTwoMember" name="SeniorNotesThreePointSixTwoFivePercentDueTwentyTwentyTwoMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SeniorNotesTwoPointNinePercentDueTwentyTwentyMember" name="SeniorNotesTwoPointNinePercentDueTwentyTwentyMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_SeriesXPreferredStockMember" name="SeriesXPreferredStockMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SevenbillionMember" name="SevenbillionMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_ShareBasedCompensationExpenseIncludedInCostsAndExpenses" name="ShareBasedCompensationExpenseIncludedInCostsAndExpenses" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_ShareBasedCompensationPlanAxis" name="ShareBasedCompensationPlanAxis" nillable="true" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_ShareBasedCompensationPlanDomain" name="ShareBasedCompensationPlanDomain" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_ShareBasedPaymentsTextualAbstract" name="ShareBasedPaymentsTextualAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_ShareOfCoPromotionProfits" name="ShareOfCoPromotionProfits" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="biib_SharesIssuedUnderEmployeeStockPurchasePlanTableTextBlock" name="SharesIssuedUnderEmployeeStockPurchasePlanTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SobiRateToBiogenOnNetSalesInSobiTerritoryMember" name="SobiRateToBiogenOnNetSalesInSobiTerritoryMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SobiTerritoryMember" name="SobiTerritoryMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SolothurnMember" name="SolothurnMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_StockOptionActivityAbstract" name="StockOptionActivityAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_StockOptionsAndEmployeeStockPurchasePlanMember" name="StockOptionsAndEmployeeStockPurchasePlanMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_StrategicInvestmentPortfolio" name="StrategicInvestmentPortfolio" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="biib_StrategicInvestmentsMember" name="StrategicInvestmentsMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_StromedixMember" name="StromedixMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_SummaryOfActivityRelatedToCollaborationWithCompanyEightTableTextBlockTableTextBlock" name="SummaryOfActivityRelatedToCollaborationWithCompanyEightTableTextBlockTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_SummaryOfActivityRelatedToCollaborationWithCompanySevenTableTextBlock" name="SummaryOfActivityRelatedToCollaborationWithCompanySevenTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_SummaryOfCommonStockTableTextBlock" name="SummaryOfCommonStockTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SummaryOfFairAndCarryingValueOfDebtInstrumentsAbstract" name="SummaryOfFairAndCarryingValueOfDebtInstrumentsAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_SummaryOfProductRevenueReservesIncludedInConsolidatedBalanceSheetsTableTextBlock" name="SummaryOfProductRevenueReservesIncludedInConsolidatedBalanceSheetsTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SummaryOfShareBasedCompensationExpenseAssociatedWithDifferentProgramsAbstract" name="SummaryOfShareBasedCompensationExpenseAssociatedWithDifferentProgramsAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SwedishOrphanBiovitrumMember" name="SwedishOrphanBiovitrumMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_TaxBenefitAndCashReceivedFromStockOptionAbstract" name="TaxBenefitAndCashReceivedFromStockOptionAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_TecfideraMember" name="TecfideraMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_TenbillionMember" name="TenbillionMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_TermOfLease" name="TermOfLease" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_Termofcollaborationagreement" name="Termofcollaborationagreement" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_ThreeBillionMember" name="ThreeBillionMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_ThresholdOfGrossSalesOfToBeAchievedInPrecedingTwelveConsecutiveMonthsUnderOptionOne" name="ThresholdOfGrossSalesOfToBeAchievedInPrecedingTwelveConsecutiveMonthsUnderOptionOne" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="biib_ThresholdOfGrossSalesToBeAchievedInAnyTwelveConsecutiveMonthsUnderOptionOne" name="ThresholdOfGrossSalesToBeAchievedInAnyTwelveConsecutiveMonthsUnderOptionOne" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="biib_TimePeriodForPayingRemainingBalanceDue" name="TimePeriodForPayingRemainingBalanceDue" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_TimeVestedRestrictedStockUnitsActivityTableTextBlock" name="TimeVestedRestrictedStockUnitsActivityTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_TimeVestedRestrictedStockUnitsMember" name="TimeVestedRestrictedStockUnitsMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_Totaldeferredchargesandprepaidtaxes" name="Totaldeferredchargesandprepaidtaxes" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="biib_TysabriMember" name="TysabriMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_TysabriProductMember" name="TysabriProductMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_UndesignatedPreferredStockMember" name="UndesignatedPreferredStockMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_UniversityofPennsylvaniaMember" name="UniversityofPennsylvaniaMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_UpfrontAndMilestonePaymentsMadeToCollaborativePartner" name="UpfrontAndMilestonePaymentsMadeToCollaborativePartner" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="biib_ValuationOfGrantedStockUnitsAbstract" name="ValuationOfGrantedStockUnitsAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_WeightedAveragePeriodToRecognizeCostOfNonvestedAwards" name="WeightedAveragePeriodToRecognizeCostOfNonvestedAwards" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_WindfallTaxBenefitsFromVestingOfStockAwardsExercisesOfStockOptionsAndEsppParticipation" name="WindfallTaxBenefitsFromVestingOfStockAwardsExercisesOfStockOptionsAndEsppParticipation" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_ZINBRYTAMember" name="ZINBRYTAMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
</xsd:schema>
