content: <?xml version="1.0" encoding="UTF-8"?><edgarSubmission xmlns="http://www.sec.gov/edgar/ownership" xmlns:com="http://www.sec.gov/edgar/common">
    <headerData>
      <submissionType>144</submissionType>
      <filerInfo>
        <filer>
          <filerCredentials>
            <cik>0001769608</cik>
            <ccc>XXXXXXXX</ccc>
          </filerCredentials>
        </filer>
        <liveTestFlag>LIVE</liveTestFlag>
  
  
  
      </filerInfo>
    </headerData>
    <formData>
      <issuerInfo>
        <issuerCik>0000875045</issuerCik>
        <issuerName>BIOGEN INC.</issuerName>
        <secFileNumber>000-19311</secFileNumber>
        <issuerAddress>
          <com:street1>225 BINNEY STREET</com:street1>
          <com:city>CAMBRIDGE</com:city>
          <com:stateOrCountry>MA</com:stateOrCountry>
          <com:zipCode>02142</com:zipCode>
        </issuerAddress>
        <issuerContactPhone>7814642000</issuerContactPhone>
        <nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>Singhal Priya</nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>
        <relationshipsToIssuer>
          <relationshipToIssuer>Officer</relationshipToIssuer>
        </relationshipsToIssuer>
      </issuerInfo>
      <securitiesInformation>
        <securitiesClassTitle>Common</securitiesClassTitle>
        <brokerOrMarketmakerDetails>
          <name>Fidelity Brokerage Services LLC</name>
          <address>
            <com:street1>900 Salem Street</com:street1>
            <com:city>Smithfield</com:city>
            <com:stateOrCountry>RI</com:stateOrCountry>
            <com:zipCode>02917</com:zipCode>
          </address>
        </brokerOrMarketmakerDetails>
        <noOfUnitsSold>108</noOfUnitsSold>
        <aggregateMarketValue>23920.92</aggregateMarketValue>
        <noOfUnitsOutstanding>145360798</noOfUnitsOutstanding>
        <approxSaleDate>02/21/2024</approxSaleDate>
        <securitiesExchangeName>NASDAQ</securitiesExchangeName>
      </securitiesInformation>
      <securitiesToBeSold>
        <securitiesClassTitle>Common</securitiesClassTitle>
        <acquiredDate>02/18/2024</acquiredDate>
        <natureOfAcquisitionTransaction>Performance Shares</natureOfAcquisitionTransaction>
        <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
        <isGiftTransaction>N</isGiftTransaction>
        <amountOfSecuritiesAcquired>108</amountOfSecuritiesAcquired>
        <paymentDate>02/18/2024</paymentDate>
        <natureOfPayment>Compensation</natureOfPayment>
      </securitiesToBeSold>
      <nothingToReportFlagOnSecuritiesSoldInPast3Months>N</nothingToReportFlagOnSecuritiesSoldInPast3Months>
      <securitiesSoldInPast3Months>
        <sellerDetails>
          <name>Priya Singhal</name>
          <address>
            <com:street1>225 Binney Street</com:street1>
            <com:city>Cambridge</com:city>
            <com:stateOrCountry>MA</com:stateOrCountry>
            <com:zipCode>02142</com:zipCode>
          </address>
        </sellerDetails>
        <securitiesClassTitle>Common</securitiesClassTitle>
        <saleDate>12/11/2023</saleDate>
        <amountOfSecuritiesSold>110</amountOfSecuritiesSold>
        <grossProceeds>27280.00</grossProceeds>
      </securitiesSoldInPast3Months>
      <securitiesSoldInPast3Months>
        <sellerDetails>
          <name>Pirya Singhal</name>
          <address>
            <com:street1>225 Binney Street</com:street1>
            <com:city>Cambridge</com:city>
            <com:stateOrCountry>MA</com:stateOrCountry>
            <com:zipCode>02142</com:zipCode>
          </address>
        </sellerDetails>
        <securitiesClassTitle>Common</securitiesClassTitle>
        <saleDate>02/02/2024</saleDate>
        <amountOfSecuritiesSold>634</amountOfSecuritiesSold>
        <grossProceeds>155919.62</grossProceeds>
      </securitiesSoldInPast3Months>
      <securitiesSoldInPast3Months>
        <sellerDetails>
          <name>Priya Singhal</name>
          <address>
            <com:street1>225 Binney Street</com:street1>
            <com:city>Cambridge</com:city>
            <com:stateOrCountry>MA</com:stateOrCountry>
            <com:zipCode>02142</com:zipCode>
          </address>
        </sellerDetails>
        <securitiesClassTitle>Common</securitiesClassTitle>
        <saleDate>02/12/2024</saleDate>
        <amountOfSecuritiesSold>419</amountOfSecuritiesSold>
        <grossProceeds>100329.55</grossProceeds>
      </securitiesSoldInPast3Months>
      <noticeSignature>
        <noticeDate>02/21/2024</noticeDate>
        <planAdoptionDates>
          <planAdoptionDate>02/23/2023</planAdoptionDate>
        </planAdoptionDates>
        <signature>/s/ Gerardo Ibarra-Munoz, as a duly authorized representative of Fidelity Brokerage Services LLC, as attorney-in-fact for Priya Singhal</signature>
      </noticeSignature>
    </formData>
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text: 144
  0001769608
  XXXXXXXX
  LIVE
  0000875045
  BIOGEN INC.
  000-19311
  225 BINNEY STREET
  CAMBRIDGE
  MA
  02142
  7814642000
  Singhal Priya
  Officer
  Common
  Fidelity Brokerage Services LLC
  900 Salem Street
  Smithfield
  RI
  02917
  108
  23920.92
  145360798
  02/21/2024
  NASDAQ
  Common
  02/18/2024
  Performance Shares
  Issuer
  N
  108
  02/18/2024
  Compensation
  N
  Priya Singhal
  225 Binney Street
  Cambridge
  MA
  02142
  Common
  12/11/2023
  110
  27280.00
  Pirya Singhal
  225 Binney Street
  Cambridge
  MA
  02142
  Common
  02/02/2024
  634
  155919.62
  Priya Singhal
  225 Binney Street
  Cambridge
  MA
  02142
  Common
  02/12/2024
  419
  100329.55
  02/21/2024
  02/23/2023
  /s/ Gerardo Ibarra-Munoz, as a duly authorized representative of Fidelity Brokerage Services LLC, as attorney-in-fact for Priya Singhal