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                     June 22, 2021

       Michael McDonnell
       Executive Vice President and Chief Financial Officer
       BIOGEN INC.
       225 Binney Street
       Cambridge, MA 02142

                                                        Re: BIOGEN INC.
                                                            Form 10-K for
Fiscal Year Ended December 31, 2020
                                                            Filed February 3,
2021
                                                            File No. 000-19311

       Dear Mr. McDonnell:

              We have completed our review of your filing. We remind you that
the company and its
       management are responsible for the accuracy and adequacy of their
disclosures, notwithstanding
       any review, comments, action or absence of action by the staff.




                     Sincerely,


                     Division of Corporation Finance

                     Office of Life Sciences