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  <xs:element id="biib_LenderDisputeMember" abstract="true" name="LenderDisputeMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="biib_AlkermesMember" abstract="true" name="AlkermesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="biib_AducanumabMember" abstract="true" name="AducanumabMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="biib_DevelopmentMilestonesMember" abstract="true" name="DevelopmentMilestonesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="biib_RegulatoryMilestonesMember" abstract="true" name="RegulatoryMilestonesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="biib_CommercialMilestonesMember" abstract="true" name="CommercialMilestonesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="biib_MilestonePaymentOneMember" abstract="true" name="MilestonePaymentOneMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="biib_MilestonePaymentTwoMember" abstract="true" name="MilestonePaymentTwoMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="biib_FutureContingentPaymentForAnnualWorldwideNetSalesUpTo2.0Billion" abstract="false" name="FutureContingentPaymentForAnnualWorldwideNetSalesUpTo2.0Billion" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
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  <xs:element id="biib_FutureContingentPaymentForAnnualWorldwideNetSalesThatExceed2.0Billion" abstract="false" name="FutureContingentPaymentForAnnualWorldwideNetSalesThatExceed2.0Billion" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
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  <xs:element id="biib_PotentialFutureMilestonePaymentsCommitmentToThirdPartyApproximately" abstract="false" name="PotentialFutureMilestonePaymentsCommitmentToThirdPartyApproximately" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
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  <xs:element id="biib_MinimumQualifyingAgeForEmployeeBenefitPlan" abstract="false" name="MinimumQualifyingAgeForEmployeeBenefitPlan" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
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  <xs:element id="biib_SegmentGeographicalGroupsOfCountriesGroupOtherMember" abstract="true" name="SegmentGeographicalGroupsOfCountriesGroupOtherMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="biib_ReportableSegmentMember" abstract="true" name="ReportableSegmentMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="biib_MilestoneAndUpfrontMember" abstract="true" name="MilestoneAndUpfrontMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
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  <xs:element id="biib_EarlyStageProgramsMember" abstract="true" name="EarlyStageProgramsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="biib_LateStageProgramsMember" abstract="true" name="LateStageProgramsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="biib_MarketedProductsMember" abstract="true" name="MarketedProductsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="biib_CollaborativeArrangementExpectedDevelopmentCostFundsYearOne" abstract="false" name="CollaborativeArrangementExpectedDevelopmentCostFundsYearOne" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="biib_CollaborativeArrangementExpectedDevelopmentCostFundsYearTwo" abstract="false" name="CollaborativeArrangementExpectedDevelopmentCostFundsYearTwo" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="biib_StephenA.SherwinMember" abstract="true" name="StephenA.SherwinMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
</xs:schema>
