State Street (STT) 10-Q 2012 Q3 Quarterly report

EXHIBIT 15

Independent Registered Public Accounting Firm’s Acknowledgment Letter

The Shareholders and Board of Directors

State Street Corporation

We are aware of the incorporation by reference in Registration Statements (Form S-3: Nos. 333-179875, 333-157882 and 333-155672, and Form S-8: Nos. 333-100001, 333-99989, 333-46678, 333-36793, 333-36409, 333-135696, 333-160171 and 333-183656) of our report dated November 2, 2012 relating to the unaudited consolidated interim financial statements of State Street Corporation that are included in its Form 10-Q for the quarter ended September 30, 2012.

Under Rule 436(c) of the 1933 Act, our report is not a part of the registration statements prepared or certified by accountants within the meaning of Section 7 or 11 of the 1933 Act.

/s/ Ernst & Young LLP

Boston, Massachusetts

November 2, 2012