Exhibit 10.66
FIRST AMENDMENT TO
EMPLOYMENT AGREEMENT
          THIS AMENDMENT by and between BIOGEN IDEC INC., (the “Company”), and
Craig Eric Schneier, Ph.D. (the “Executive”), dated as of September ___, 2008.
          WHEREAS, the Executive and the Company are parties to an Employment
Agreement dated as of October 8, 2001 (the “October 8, 2001 Agreement”); and
          WHEREAS, the Executive and the Company desire to amend the October 8,
2001 Agreement as set forth herein.
          NOW, THEREFORE, it is hereby agreed as follows:

  1.   The following sentence is added to the first full paragraph of the
October 8, 2001 Agreement

      “It is a condition of your employment with the Company that Jim Mullen
will be President and Chief Executive Officer during your tenure with the
Company.”

  2.   The paragraph relating to “Severance Benefits” is hereby amended and
restated by the replacement in full with the following:

      “- Severance Benefits: You will be eligible for severance benefits
pursuant to the U.S. Severance Plan for Executive Vice Presidents (the
“Severance Plan”) on the terms and conditions provided therein; provided,
however, that you will also be eligible for benefits thereunder in the event
that you terminate your employment on account of a material breach of the
provision in this letter in that Jim Mullen is no longer President and Chief
Executive Officer of the Company. You will not be an employee of Biogen during
the severance period and you will not accrue any benefits or other rights (such
as, but not limited to, pension plan vesting or accrual, stock option vesting,
vacation pay, etc.) during such period except health benefits as described in
the “Severance Plan”. In addition to the severance benefits described above, the
unforgiven amount of the Forgivable Loan referenced on the first page of this
letter would be forgiven based on the definition of termination as noted
herein.”

Signed:

             
/s/ Craig Eric Schneier
 
Craig Eric Schneier, Ph.D. (Executive)
         10/8/08
 
Date    
 
           
/s/ Mike Thomas
         10/7/08    
 
           
Mike Thomas (on behalf of the Company)
      Date