Exhibit 23

                    [Deloitte & Touche LLP Letterhead]

         CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We consent to the incorporation by reference in Registration Statement No.
333-75848 of Marshall & Ilsley Corporation on Form S-8 of our reports dated
June 26, 2006, appearing in this Annual Report on Form 11-K of the M&I
Retirement Program (consisting of the M&I Retirement Plan and Employee Stock
Ownership Plan) for the year ended December 31, 2005.


/s/ DELOITTE & TOUCHE LLP


Milwaukee, Wisconsin
June 26, 2006