An initial term that ends on December 31, 2019 (the
Employment Term). On each December 31 beginning December
31, 2019, the Employment Term will automatically be
extended for an additional year unless either party gives
the other notice by the preceding July 1 that it has
elected not to extend the Employment Term. Notwithstanding
the foregoing, Mr. Vounatsos will be an employee at will
whose employment can be terminated at any time by either
party. Mr. Vounatsos is prohibited from competing with
Biogen during his employment and for twelve months after
the termination of his employment for any reason.

An annual base salary at the initial rate of $1,100,000,
subject to annual review and potential merit increases. The
annual base salary cannot be reduced without Mr. Vounatsos
consent except for across the board decreases applicable in
the same percentage to all senior executives and in an
aggregate amount of not more than 10%.

Participation in Biogens 2008 Performance-Based Management
Incentive Plan, or such other annual bonus plan as Biogen
may adopt, with a target annual bonus opportunity of not
less than 125% of his base salary. Mr. Vounatsos annual
bonus for 2016 will be based on his prior position.

Participation in Biogens 2008 Omnibus Equity Plan (OEP) or
such long term incentive plan as Biogen may establish in
its place. In 2017 Mr. Vounatsos will receive long-term
incentive awards with a grant date value of $10,000,000.
Fifty percent (50%), or $5,000,000, of the grant date value
will be in the form of Cash-Settled Performance Shares and
50%, or $5,000,000, will be in the form of Market Stock
Units, as such terms are defined in the OEP.

Upon a termination of employment for any reason, Mr.
Vounatsos is entitled to receive his base salary accrued
through the date of termination, the value of his unused
vacation time, reimbursement of business expenses properly
incurred prior to termination, and any amounts payable upon
termination under Biogens employee benefit plans and
policies (the Accrued Obligations).

Upon a termination of employment on account of death or
disability, Mr. Vounatsos, or his beneficiary in the case
of death, will receive, in addition to the Accrued
Obligations, his unpaid

Upon a termination of employment due to an Involuntary
Employment Action that occurs either prior to, or more than
two years after, a Change in Control (as defined in the
OEP), Mr. Vounatsos will receive, in addition to the
Accrued Obligations, his unpaid annual bonus for the prior
year to the extent not yet paid, a pro rata share of his
annual bonus for the year in which the termination occurs
(based on the extent to which the corporate performance
goals are actually achieved for the year), a severance
payment equal to one and a half times the sum of his base
salary and target annual bonus, paid in a lump sum within
60 days after termination, medical coverage at the premium
rates paid by active employees for up to 18 months after
the termination date, and senior executive level career
transition services for up to 12 months after the
termination date. For this purpose, an Involuntary
Employment Action includes a termination by Biogen without
cause (as defined in the Employment Agreement), or
resignation by Mr. Vounatsos after the occurrence of
certain events described in the Employment Agreement, if
Biogen fails to cure such events after receiving notice
from Mr. Vounatsos. Payment of such benefits (other than
the Accrued Obligations) is subject to Mr. Vounatsos
signing a release of claims against Biogen in the form
appended to the Employment Agreement.

Upon a termination of employment due to an Involuntary
Employment Action that occurs within two years after a
Change in Control, Mr. Vounatsos will receive the same
benefits described in the preceding paragraph, except that
the pro rata annual bonus will be based on his target
bonus, the lump sum severance payment will be equal to two
times the sum of his base salary and target bonus, and the
period during which he may continue medical coverage at
active employee premium rates will continue for up to
twenty-four months. If a Change in Control occurs within
six months following an Involuntary Employment Action, he
will receive the benefits described in this paragraph,
reduced by any benefits previously paid at the time of the
original Involuntary Employment Action.

An expiration of the Employment Term is not considered an
Involuntary Employment Action, but Mr. Vounatsos would be
entitled to the Accrued Obligations and his annual bonus
for the year ending on the date of expiration. If the
expiration results from Biogens election not to extend the
Employment Term, it would be treated as an involuntary
termination for purposes of any plan or program that
conditions payment of benefits upon an involuntary
termination.

The vesting and payment of Mr. Vounatsos equity awards upon
a termination of employment will be governed by the terms
of the applicable award and plan and will not be affected
by the Employment Agreement, except that the definitions of
cause, disability, and Involuntary Employment Action
contained in the Employment Agreement will also apply for
purposes of such awards.

During 2017, Mr. Vounatsos will invest $1,000,000 in Biogen
common stock.

Biogen will reimburse Mr. Vounatsos for his attorneys fees
incurred in the negotiation of the Employment Agreement to
a maximum of $30,000.