United states securities and exchange commission

Table of Contents
BIOGEN INC. AND SUBSIDIARIES
NOTES TO CONSOLIDATED FINANCIAL STATEMENTS — (Continued)
F- 47
The fair values of MSUs vested in 2017, 2016 and 2015 totaled $31.4 million, $39.3 million and $109.0 
million, respectively.
Cash Settled Performance Units (CSPUs)
CSPUs awarded to employees vest in three equal annual increments beginning on the first anniversary of the 
grant date. The vesting of these awards is subject to the respective employee’s continued employment with such 
awards settled in cash. The number of CSPUs granted represents the target number of units that are eligible to be 
earned based on the attainment of certain performance measures established at the beginning of the performance 
period, which ends on December 31 of each year. Participants may ultimately earn between 0% and 200% of the 
target number of units granted based on the degree of actual performance metric achievement. Accordingly, 
additional CSPUs may be issued or currently outstanding CSPUs may be cancelled upon final determination of the 
number of units earned. CSPUs awarded prior to 2014 are settled in cash based on the 60 calendar day average 
closing stock price through each vesting date once the actual vested and earned number of units is known. CSPUs 
awarded in 2014 and thereafter will be settled in cash based on the 30 calendar day average closing stock price 
through each vesting date, once the actual vested and earned number of units is known. Since no shares are issued, 
these awards do not dilute equity. Compensation expense, including the effect of forfeitures, is recognized over the 
applicable service period.
The following table summarizes our CSPU activity:
Shares
Unvested at December 31, 2016
122,000
Hemophilia spin-off adjustment
3,000
Granted (a)
83,000
Vested
(69,000)
Forfeited
(34,000)
Unvested at December 31, 2017
105,000
(a) 
CSPUs granted in 2017 include awards granted in conjunction with our annual awards made in February 2017 and CSPUs 
granted in conjunction with the hiring of employees. These grants reflect the target number of shares eligible to be earned 
at the time of grant. CSPUs granted in 2017 also include CSPUs issued in 2017 based upon the attainment of performance 
criteria set for 2016 in relation to shares granted in 2016.
The cash paid in settlement of CSPUs vested in 2017, 2016 and 2015 totaled $16.6 million, $31.9 million 
and $79.8 million, respectively.  
Performance-vested Restricted Stock Units (PUs)
PUs are granted to certain employees in the form of RSUs that may be settled in cash or shares of our common 
stock at the sole discretion of the Compensation and Management Development Committee of our Board of 
Directors. These awards are structured and accounted for the same way as the CSPUs, and vest in three equal 
annual increments beginning on the first anniversary of the grant date. The number of PUs granted represents the 
target number of units that are eligible to be earned based on the attainment of certain performance measures 
established at the beginning of the performance period, which ends on December 31 of each year. Participants may 
ultimately earn between 0% and 200% of the target number of units granted based on the degree of actual 
performance metric achievement. Accordingly, additional PUs may be issued or currently outstanding PUs may be 
cancelled upon final determination of the number of units earned. PUs settling in cash are based on the 30 calendar 
day average closing stock price through each vesting date once the actual vested and earned number of units is 
known. Compensation expense, including the effect of forfeitures, is recognized over the applicable service period.

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Table of Contents
BIOGEN INC. AND SUBSIDIARIES
NOTES TO CONSOLIDATED FINANCIAL STATEMENTS — (Continued)
F- 48
The following table summarizes our PU activity:
Shares
Unvested at December 31, 2016
110,000
Hemophilia spin-off adjustment
3,000
Granted (a)
40,000
Vested
(43,000)
Forfeited
(19,000)
Unvested at December 31, 2017
91,000
(a)  PUs granted in 2017 include awards granted in conjunction with our annual awards made in February 2017 and PUs granted 
in conjunction with the hiring of employees. These grants reflect the target number of shares eligible to be earned at the 
time of grant.
During 2015 32,000 PUs were converted to share settlements, of which approximately 11,000 shares were 
vested and issued. All other PUs that vested in 2015 were settled in cash totaling $12.4 million.
All PUs that vested in 2017 and 2016 were settled in cash totaling $11.5 million and $8.1 million, respectively.
Time-Vested Restricted Stock Units (RSUs)
RSUs awarded to employees generally vest no sooner than one-third per year over three years on the 
anniversary of the date of grant, or upon the third anniversary of the date of the grant, provided the employee 
remains continuously employed with us, except as otherwise provided in the plan. Shares of our common stock will 
be delivered to the employee upon vesting, subject to payment of applicable withholding taxes. RSUs awarded to 
directors for service on our Board of Directors vest on the first anniversary of the date of grant, provided in each 
case that the director continues to serve on our Board of Directors through the vesting date. Shares of our common 
stock will be delivered to the director upon vesting and are not subject to any withholding taxes. The fair value of all 
RSUs is based on the market value of our stock on the date of grant. Compensation expense, including the effect of 
forfeitures, is recognized over the applicable service period.
The following table summarizes our RSU activity:
Shares
Weighted
Average
Grant Date
Fair Value
Unvested at December 31, 2016
888,000 $
303.49
Hemophilia spin-off adjustment
12,000 $
—
Granted (a)
464,000 $
293.41
Vested
(350,000) $
308.04
Forfeited
(182,000) $
292.57
Unvested at December 31, 2017
832,000 $
291.85
(a) 
RSUs granted in 2017 primarily represent RSUs granted in conjunction with our annual awards made in February 2017 and 
awards made in conjunction with the hiring of new employees. RSUs granted in 2017 also include approximately 11,000 
RSUs granted to our Board of Directors.
RSUs granted in 2016 and 2015 had weighted average grant date fair values of $268.52 and $388.88, 
respectively.
The fair values of RSUs vested in 2017, 2016 and 2015 totaled $100.0 million, $104.6 million and $239.7 
million, respectively.  

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