Exhibit 23.1

Consent of Independent Registered Public Accounting Firm

We consent to the incorporation by reference in the Registration Statement (Form S-8) pertaining to the 2007 Equity Incentive Plan and 2007 Employee Stock Purchase Plan of ArcSight, Inc. of our report dated July 17, 2008, with respect to the consolidated financial statements of ArcSight, Inc. included in its Annual Report (Form 10-K) for the year ended April 30, 2008, filed with the Securities and Exchange Commission.

/s/ Ernst & Young LLP San Jose, California
January 8, 2009