VERTEX PHARMACEUTICALS INCORPORATED EMPLOYEE STOCK PURCHASE PLAN

Exhibit 10.1

VERTEX PHARMACEUTICALS INCORPORATED
EMPLOYEE STOCK PURCHASE PLAN
(as amended and restated)

ARTICLE 1
PURPOSE AND DEFINITIONS

        SECTION 1.1.     PURPOSE.    The purpose of the Vertex Pharmaceuticals Incorporated Employee Stock Purchase Plan is to provide employees with an opportunity to purchase Common Stock in the Company through payroll deductions, thereby encouraging employees to share in the economic growth and success of the Company through stock ownership.

        SECTION 1.2.     DEFINITIONS.    Whenever used in the Plan, unless the context clearly indicates otherwise, the following terms shall have the following meanings:

• (a)

  "BENEFICIARY" with respect to a Participant, means the beneficiary designated by the Participant under the group term life insurance plan maintained by the Company or such other beneficiary as may be designated by a Participant for purposes of this Plan.
  
  

  (b)

  "BOARD OF DIRECTORS" means the Board of Directors of the Company.
  
  

  (c)

  "CODE" means the Internal Revenue Code of 1986, as the same may be amended from time to time, and references thereto shall include the valid Treasury regulations issued thereunder.
  
  

  (d)

  "COMMITTEE" means the Management Development and Compensation Committee of the Board of Directors or such other committee of the Board of Directors designated by the Board of Directors to administer the Company's equity compensation plans.
  
  

  (e)

  "COMMON STOCK" means shares of the $.01 par value common stock of the Company and any other stock or securities resulting from the adjustment thereof or substitution therefor as described in Section 3.4.
  
  

  (f)

  "COMPANY" means Vertex Pharmaceuticals Incorporated or any successor by merger, purchase, or otherwise.
  
  

  (g)

  "COMPENSATION" means the cash compensation received by an Employee for services, including pre-tax employee compensation made to the Company's 401(k) savings plan, but not including overtime or bonuses.
  
  

  (h)

  "EFFECTIVE DATE" means July 1, 1992.
  
  

  (i)

  "ELECTION" means an election by a Participant to terminate an Offering Period on the first Purchase Date of such Offering Period, which election shall be made within such Offering Period and prior to such First Purchase Date and shall be in writing on a form furnished by the Company for such purpose and shall be made by having such Participant complete, sign and file such form with the Company in the manner prescribed by the Company.
  
  

  (j)

  "EMPLOYEE" means any person who receives a regular stated compensation from the Company or a Subsidiary other than a pension, severance pay, retainer, or fee under contract.
  
  

  (k)

  "FAIR MARKET VALUE" of a Share of Common Stock on a particular date shall be the average of the highest and lowest quoted selling prices on such date (the "valuation date") on the securities market where the Common Stock of the Company is traded, or if there were no sales on the valuation date, on the next preceding date within a reasonable period (as

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• • determined in the sole discretion of the Committee) on which there were sales. In the event that there were no sales in such a market within a reasonable period, the fair market value shall be as determined in good faith by the Committee in its sole discretion. The Fair Market Value as determined in this paragraph shall be rounded down to the next lower whole cent if the foregoing calculation results in fractional cents.

  (l)

  "OFFERING" means the offering of shares of Common Stock to Participants pursuant to this Plan.
  
  

  (m)

  "OFFERING DATE" means each May 15 and November 15. If any such date shall fall other than on a business day, then the Offering Date shall be the next succeeding business day.
  
  

  (n)

  "OFFERING PERIOD" means either (i) the period from an Offering Date through the second Purchase Date following such Offering Date or (ii) if a Participant validly exercises an Election, the period from an Offering Date through the first Purchase Date following such Offering Date.
  
  

  (o)

  "PARTICIPANT" means an Employee who has elected to participate in the Plan.
  
  

  (p)

  "PURCHASE DATE" means each May 14 and November 14.
  
  

  (q)

  "PLAN" means the Vertex Pharmaceuticals Incorporated Employee Stock Purchase Plan, an "employee stock purchase plan" within the meaning of Section 423(b) of the Code, together with any and all amendments thereto.
  
  

  (r)

  "STOCK PURCHASE ACCOUNT," with respect to a Participant, means the account established on the books and records of the Company or a Subsidiary for such Participant representing the payroll deductions credited to such account in accordance with the provisions of the Plan.
  
  

  (s)

  "SUBSIDIARY" means any corporation, fifty percent (50%) or more of the total combined voting power of all classes of stock of which is beneficially owned, directly or indirectly, by the Company.

ARTICLE II
PARTICIPATION

        SECTION 2.1.     PARTICIPATION REQUIREMENTS.    

• (a)

  COMMENCEMENT OF PARTICIPATION.    Subject to Section 2.2 and Section 3.2(b), each person who becomes an Employee after the Effective Date may become a Participant in the Plan on any Offering Date following the date on which such person becomes an Employee.
  
  

  (b)

  ELIGIBILITY OF FORMER PARTICIPANTS.    If a person terminates employment with the Company after becoming a Participant and subsequently resumes employment with the Company, such person will again become eligible to participate on the Offering Date next following such resumption of employment with the Company.

        SECTION 2.2.     EXCLUSIONS.     Notwithstanding any provision of the Plan to the contrary, in no event shall the following persons be eligible to participate in the Plan:

• (a)

  Any Employee whose customary employment is twenty (20) hours or less per week;
  
  

  (b)

  Any Employee whose customary employment is for not more than five (5) months in any calendar year; or
  
  

  (c)

  Any Employee who, as of the beginning of an Offering Period, owns (or under Section 423(b)(3) of the Code would be deemed to own) stock possessing five percent (5%)

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• • or more of the total combined voting power or value of all classes of stock of the Company or a Subsidiary.

ARTICLE III
OFFERING OF COMMON STOCK

        SECTION 3.1.     RESERVATION OF COMMON STOCK.    The Board of Directors shall reserve 1,748,660 shares of Common Stock for issuance under the Plan after March 17, 2004, subject to adjustment in accordance with Section 3.4, provided that no more than 248,660 of such shares shall be issued prior to May 15, 2004. On May 13, 2008, the Board of Directors shall reserve an additional 2,000,000 shares of Common Stock for issuance under the Plan.

        SECTION 3.2.     OFFERING OF COMMON STOCK.    

• (a)

  GENERAL.    Subject to Section 3.2(b), each Participant in the Plan on an Offering Date shall be entitled to purchase shares of Common Stock on each Purchase Date within the Offering Period that begins with such Offering Date with the amounts deducted from such Participant's Compensation during such Offering Period pursuant to Article IV, provided, however, that a Participant shall not participate in more than one Offering Period simultaneously. The purchase price for such shares of Common Stock shall be determined under Section 3.3.
  
  

  (b)

  LIMITATIONS.    Notwithstanding Section 3.2(a), no employee may accrue rights to purchase shares of Common Stock attributable to an Offering Period in excess of $25,000 of fair market value of such shares (measured as of the relevant Offering Date) for each calendar year during which such rights are outstanding. For any year, this limit shall be further reduced by the fair market value of stock (measured as of the relevant Offering Date for such stock) purchasable under any prior outstanding rights relating to such calendar year under this Plan and all other Code section 423 employee stock purchase plans of the Company or any Subsidiary. This paragraph is intended to be consistent with the limitation of Code section 423(b)(8) and shall be interpreted accordingly.

        SECTION 3.3.     DETERMINATION OF PURCHASE PRICE FOR OFFERED COMMON STOCK.    The purchase price per share of the shares of Common Stock to be acquired by a Participant on a Purchase Date pursuant to an Offering shall be equal to eighty-five percent (85%) of the lesser of:

• (a)

  the Fair Market Value of a share of Common Stock on the Offering Date for such Offering Period; or
  
  

  (b)

  the Fair Market Value of a share of Common Stock on such Purchase Date;

        provided, however, in no event shall the purchase price be less than the par value of a share of Common Stock.

        SECTION 3.4.     EFFECT OF CERTAIN TRANSACTIONS.    The number of shares of Common Stock reserved for the Plan pursuant to Section 3.1, the maximum number of shares of Common Stock offered pursuant to Section 3.2(b), and the determination under Section 3.3 of the purchase price per share of the shares of Common Stock offered to Participant