UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the

Securities Exchange Act of 1934

Date of Report

(Date of earliest event reported): August 12, 2011

This combined Form 8-K is separately filed by Alliant Energy Corporation, Interstate Power and Light Company and Wisconsin Power and Light Company.

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Alliant Energy Corporation (“Alliant Energy”), Interstate Power and Light Company (“IPL”) and Wisconsin Power and Light Company (“WPL”, and together with Alliant Energy and IPL, the “Company”) announced the retirement of Dundeana K. Doyle, Senior Vice President – Energy Delivery (“Executive”), effective August 31, 2011. On August 12, 2011, the Compensation and Personnel Committee of the Board of Directors (the “Committee”) approved a retirement package that included, and the Company entered into, an Executive Agreement, which provides a cash payment of $291,400 and provides up to $10,000 in outplacement services or tuition reimbursement to Executive (the “Agreement”). Under the Agreement, Executive agreed to a one-year covenant not to compete, not to disparage the Company and to keep information regarding the Company confidential, and a general release. The Committee also approved an amendment to the Supplemental Retirement Plan Agreement (“SERP”) between Executive and Alliant Energy to vest payment of the supplemental benefit at age 53.5, which will result in a payment of approximately $1,535,000 to Executive. Any other payments due to Executive as a result of her retirement are payable pursuant to the terms of other previously existing arrangements and have not been changed in connection with her retirement. A copy of the Agreement is attached as Exhibit 10.1, and a copy of the amendment to the SERP is attached as Exhibit 10.2, to this Current Report on Form 8-K and both are incorporated herein by reference.

(10.1) Executive Agreement between Company and Executive dated August 12, 2011

(10.2) Amendment to Supplemental Retirement Plan Agreement between Executive and Alliant Energy Corporation dated August 12, 2011

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SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, Alliant Energy Corporation, Interstate Power and Light Company and Wisconsin Power and Light Company have each duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

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EXHIBIT INDEX

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