Form of Nonstatutory Stock Option Agreement

Exhibit 10.23


Achillion Pharmaceuticals, Inc.

Nonstatutory Stock Option Agreement

Granted Under 2006 Stock Incentive Plan


1. Grant of Option .

This agreement evidences the grant by Achillion Pharmaceuticals, Inc. a Delaware corporation (the " Company" ), on [ ] , 200[ ] (the " Grant Date" ) to [ ], an [employee,] [consultant,] [director] of the Company (the " Participant" ), of an option to purchase, in whole or in part, on the terms provided herein and in the Company' s 2006 Stock Incentive Plan (the " Plan" ), a total of [ ] shares (the " Shares" ) of common stock, [ ] par value per share, of the Company (" Common Stock" ) at $[ ] per Share. Unless earlier terminated, this option shall expire at 5:00 p.m., Eastern time, on [ ] (the " Final Exercise Date" ).

It is intended that the option evidenced by this agreement shall not be an incentive stock option as defined in Section 422 of the Internal Revenue Code of 1986, as amended, and any regulations promulgated thereunder (the " Code" ). Except as otherwise indicated by the context, the term " Participant" , as used in this option, shall be deemed to include any person who acquires the right to exercise this option validly under its terms.


2. Vesting Schedule .

This option will become exercisable (" vest" ) as to % of the original number of Shares on the first anniversary of the Grant Date and as to an additional % of the original number of Shares at the end of each successive [ three-month] period following the [first] anniversary of the Grant Date until the [fourth] anniversary of the Grant Date.

The right of exercise shall be cumulative so that to the extent the option is not exercised in any period to the maximum extent permissible it shall continue to be exercisable, in whole or in part, with respect to all Shares for which it is vested until the earlier of the Final Exercise Date or the termination of this option under Section 3 hereof or the Plan.


3. Exercise of Option .


(a) Form of Exercise . Each election to exercise this option shall be in writing, signed by the Participant, and received by the Company at its principal office, accompanied by this agreement, and payment in full in the manner provided in the Plan. A form of Notice of Stock Option Exercise is attached as Exhibit A . The Participant may purchase less than the number of shares covered hereby, provided that no partial exercise of this option may be for any fractional share or for fewer than ten whole shares.

(b) Continuous Relationship with the Company Required . Except as otherwise provided in this Section 3, this option may not be exercised unless the Participant, at the time he or she exercises this option, is, and has been at all times since the Grant Date, an employee or officer or director of, or consultant or advisor to, the Company or any other entity the employees,

officers, directors, consultants, or advisors of which are eligible to receive option grants under the Plan (an " Eligible Participant" ).


(c) Termination of Relationship with the Company . If the Participant ceases to be an Eligible Participant for any reason, then, except as provided in paragraphs (d) and (e) below, the right to exercise this option shall terminate three months after such cessation (but in no event after the Final Exercise Date), provided that this option shall be exerci ...