Exhibit 15

PricewaterhouseCoopers LLP

PricewaterhouseCoopers Center

300 Madison Avenue

New York NY 10017

Telephone (646) 471 3000

Facsimile (813) 286 6000

May 8, 2008

Securities and Exchange Commission

100 F Street, N.E.

Washington, DC 20549

Commissioners:

We are aware that our report dated May 8, 2008 on our review of interim financial information of Arch Capital Group Ltd. and its subsidiaries (the “Company”) for the three month period ended March 31, 2008 and 2007 and included in the Company’s quarterly report on Form 10-Q for the quarter ended March 31, 2008 is incorporated by reference in the Registration Statement on Forms S-3 (Registration No. 33-34499, Registration No. 333-82612, Registration No. 333-110190, Registration No. 333-117099 and Registration No. 333-135421) and in the Registration Statements on Forms S-8 (Registration No. 33-99974, Registration No. 333-86145, Registration No. 333-72182, Registration No. 333-82772, Registration No. 333-98971, Registration No. 333-124422 and Registration No. 333-142835).

Very truly yours,

/s/ PricewaterhouseCoopers LLP