EXHIBIT 10.51

ARIBA BONUS PLAN

EXECUTIVE OFFICERS

1. Effective Date and Term. This Plan was adopted by the Compensation Committee
(the “Committee”) of the Board of Directors of Ariba, Inc. (the “Company”) on
November 15, 2007 and amended on April 16 , 2008. The Plan, as amended, is
effective for fiscal year 2008 and thereafter will continue to apply until it is
amended or terminated by the Committee. It supersedes all prior bonus plans
applicable to individuals who are deemed to be “officers” of the Company for
purposes of Section 16 of the Securities Exchange Act of 1934, as amended (the
“Executive Officers”). Any other bonus plan applicable to Executive Officers
previously approved by the Committee is hereby terminated.

2. Administration. The Committee administers the Plan and adopts rules and
regulations to implement the Plan. The decisions of the Committee are final and
binding on all parties who have an interest in the Plan.

3. Eligibility. Participation in the Plan is limited to Executive Officers.
Participation in the Plan is effective on the day the participant starts in a
bonus-eligible job. Participants must be employed in a bonus-eligible position
before the first day of the last month of the fiscal year to be eligible to
participate in the Plan for that fiscal year. Bonus payments will be prorated
for participants who become eligible after the start of a fiscal year or for
participants who are on a leave of absence or sabbatical for all or part of a
fiscal year. A participant may be removed from the Plan at any time and for any
reason, at the Company’s discretion, regardless of whether he or she remains an
officer or employee of the Company.

4. Determination of Amounts. The Plan may provide an annual cash bonus that is
paid based on the achievement of pre-determined Company performance objectives
and individual performance factors. The amount of each participant’s annual
bonus is determined as follows:

(a) An annual target bonus amount is assigned to the participant by the
Committee as soon as reasonably practicable after the beginning of a fiscal year
or, if later, at the time of his or her hiring. The annual target bonus amount
may be modified from time to time thereafter by the Committee.

(b) Except in the case of the President, one-half of the annual bonus is
determined on the basis of the Company’s annual non-GAAP net income score and
one-half is determined on the basis of the Company’s annual non-GAAP revenue
score. “Non-GAAP net income” means after-tax income excluding
(i) restructuring-related expense, (ii) amortization of acquired core technology
and in-process R&D, (iii) amortization of goodwill and intangibles,
(iv) amortization of stock-based compensation; and (v) purchase accounting
adjustment-deferred revenue. “Non-GAAP revenue” means revenue excluding the
impact of purchase accounting adjustment-deferred revenue.

(c) As soon as reasonably practicable after the beginning of a fiscal year, the
Committee determines for that year the levels of non-GAAP net income and
non-GAAP revenue that will be required for non-GAAP net income and non-GAAP
revenue scores of 0.50, 0.75, 1.00 and 2.00. If the level of non-GAAP net income
or non-GAAP revenue is less than the level required for a 0.50 score, the score
will be zero. If the level of non-GAAP net income or non-GAAP revenue is greater
than the amount required for a 2.00 score, the score will be 2.00. If the amount
of non-GAAP net income or non-GAAP revenue falls between the amounts required
for a 0.50 score and a 0.75 score, between the amounts required for a 0.75 score
and a 1.00 score or between the amounts required for a 1.00 score and a 2.00
score, then straight-line interpolation will be used.

(d) When the amount of non-GAAP net income for a fiscal year has been
determined, the non-GAAP net income score is calculated. Likewise, when the
amount of non-GAAP revenue for a fiscal year has been determined, the non-GAAP
revenue score is calculated. The weighted-average score for the fiscal year
equals one-half of the non-GAAP net income score plus one-half of the non-GAAP
revenue score. This weighted-average score is multiplied by each participant’s
annual target bonus amount.

--------------------------------------------------------------------------------

(e) After the close of the fiscal year, the Committee at its discretion may
increase or reduce any annual bonus based on criteria other than non-GAAP net
income and non-GAAP revenue (including individual performance).

(f) In the case of the President, the Company’s annual bookings score is added
to the other two scores described above. The annual bookings score has a weight
of 20%, the non-GAAP net income score has a weight of 40%, and the non-GAAP
revenue score has a weight of 40%. As soon as reasonably practicable after the
beginning of the fiscal year, the Committee determines the amount of bookings
that will be required for bookings scores of 0.50, 0.75, 1.00 and 2.00. If the
amount of bookings is less than the amount required for a 0.50 score, the score
will be zero. If the amount of bookings is greater than the amount required for
a 2.00 score, the score will be 2.00. If the amount of bookings falls between
the amounts required for a 0.50 score and a 0.75 score, between the amounts
required for a 0.75 score and a 1.00 score or between the amounts required for a
1.00 score and a 2.00 score, then straight-line interpolation will be used. All
other provisions of the Plan apply to the President in the same manner as to the
other Executive Officers.

(g) The Committee may adjust the amount of the Company’s annual non-GAAP net
income or annual non-GAAP revenue, or both, to exclude extraordinary expenses or
benefits.

5. Payment of Bonuses. Payment of the annual cash bonus (if any) is targeted for
November 30. Adjustments to this payment schedule may be made as business
conditions require.

6. Employment Requirement. Unless a Severance Agreement between a participant
and the Company provides otherwise, the participant must be employed by the
Company at the time of the bonus payment to receive the annual cash bonus.

7. Modification or Termination of the Plan. The Committee reserves the right to
modify, suspend or terminate this Plan at any time. Should an acquisition or
significant business initiative change the operating plan, this Plan may be
modified or a new plan may go into effect following this event.

8. Benefits Unfunded. No amounts awarded or accrued under this Plan will be
funded, set aside or otherwise segregated prior to payment. The obligation to
pay the bonuses awarded hereunder will at all times be an unfunded and unsecured
obligation of the Company. Plan participants will have the status of general
creditors and must look solely to the general assets of the Company for the
payment of their bonus awards.

9. Benefits Nontransferable. No Plan participant will have the right to
alienate, pledge or encumber his or her interest in this Plan, and such interest
will not (to the extent permitted by law) be subject in any way to the claims of
the participant’s creditors or to attachment, execution or other process of law.

10. No Employment Rights. No action of the Company in establishing the Plan, no
action taken under the Plan by the Committee and no provision of the Plan itself
will be construed to grant any person the right to remain in the employ of the
Company or its subsidiaries for any period of specific duration. Rather, each
employee is employed “at will,” which means that either the employee or the
Company may terminate the employment relationship at any time and for any
reason, with or without cause.