Exhibit 10.1

January 5, 2005

William H. Rastetter, Ph.D.
Executive Chairman
Biogen Idec Inc.

Re:  Use of Company-Owned Condominium

Dear Bill:

     This letter sets forth our agreement as to your use of a company-owned
condominium in Cambridge, Massachusetts. You acknowledge that you have been
using the condominium since January 2004 and that this agreement covers your use
of the condominium since that time as well as future use. The primary reason
that the condominium is being provided to you is for lodging when you come to
Cambridge for business purposes.

     As the owner of the condominium, the company reserves the right to use the
condominium for company functions and other activities at the company’s
discretion and at times when such use does not interfere with your business
visits to Cambridge.

     The condominium is to be used by you primarily for business purposes, i.e.,
lodging when you are away from your principal place of business in San Diego,
California and in Cambridge performing services for the company. Limited
incidental personal use of the condominium by you or by your spouse (or
significant other), when accompanied by you, is permitted. You must report such
personal use to the company within 30 days. The fair rental value of such
personal use of the condominium will be added to your compensation, grossed up
for the appropriate taxes, treated as wages for payroll tax purposes, and
reported on Form W-2.

     As owner, the company will pay the costs and expenses of the condominium
including taxes, condominium fees, insurance for real and personal property,
utilities, cleaning, maintenance, renovations, repairs, and such other costs and
expenses as are assessed or expected by the condominium association from time to
time. Since you will be the principal business lodger of the condominium, the
company will provide you with a list of approved service providers to perform
cleaning, maintenance, renovation and repair services at times convenient to
your visits. The approved service providers will bill the company directly for
services related to the condominium. Costs and expenses of unapproved service
providers will be your financial responsibility unless the company agrees to pay
such costs and expenses. You agree to promptly provide the company with original
invoices and bills, with appropriate explanations, for company-covered costs and
expenses that are sent directly to the condominium.

 

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     The company shall own the portion of the furniture, equipment, furnishings,
decorations and similar items in the condominium for which it pays and you shall
own the rest.

     You agree at all times to maintain the condominium in good, clean and
livable condition, normal wear and tear excepted.

     Your use of the condominium is solely at the discretion of the company. The
company may terminate your use of the condominium at anytime upon 30 days
written notice to you. In addition, if your employment with the company ends for
any reason, your use of the condominium will terminate on your last day of
employment with the company.

     
 
   
Very truly yours,
   
 
   
/s/ Craig Eric Schneier
   
 
   
 
   
Craig Eric Schneier
   
Executive Vice President, Human Resources
   
 
 
   
Acknowledged and Agreed:
   
 
   
/s/ William H. Rastetter
   
 
   
 
   
William H. Rastetter, Ph.D.,
   
 Executive Chairman
   

cc:  Bruce R. Ross, Chair, Compensation
  and Management and Development Committee

Alan Belzer, Chair, Corporate
  Governance Committee

Thomas F. Keller, Chair, Finance
  and Audit Committee