As filed with the Securities and Exchange Commission on March 31,April 9, 2004

Registration No. 333-______     

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

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FORM S-3
REGISTRATION STATEMENT
Under
THE SECURITIES ACT OF 1933

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ALLIANT ENERGY CORPORATION
(Exact name of registrant as specified in its charter)

Alliant Energy Corporation
4902 North Biltmore Lane
Madison, Wisconsin 53718-2132
(608) 458-3311
(Address, including zip code, and telephone number, including area code, of registrant’s principal executive offices)

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        Approximate date of commencement of proposed sale to the public: From time to time after this registration statement becomes effective.

        If the only securities being registered on this Form are being offered pursuant to dividend or interest reinvestment plans, please check the following box.  |_|

        If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, other than securities offered only in connection with dividend or interest reinvestment plans, please check the following box.  |X|

        If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.  |_|

        If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.  |_|

        If delivery of the prospectus is expected to be made pursuant to Rule 434, please check the following box.  |_|

(1)     Each share of Alliant Energy Corporation Common Stock has attached thereto one Common Share Purchase Right.

(2)     Estimated solely for the purpose of calculating the registration fee pursuant to Rule 457(c) under the Securities Act of 1933, based on the average of the high and low prices of the Common Stock of Alliant Energy Corporation as reported on the New York Stock Exchange on April 25, 2004. The value attributable to the Rights is reflected in the price of the Common Stock.

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        Pursuant to Rule 429 under the Securities Act of 1933, the Prospectus which is a part of this Registration Statement includes all the information currently required in a prospectus relating to the securities covered by Registration Statements Nos. 333-26627, 333-101209 and 333-101307 of the Registrant. This Registration Statement also constitutes Post-Effective Amendment No. 1 with respect to each of Registration Statements Nos. 333-26627, 333-101209 and 333-101307 and such post-effective amendments shall thereafter become effective concurrently with the effectiveness of this Registration Statement in accordance with Section 8(c) of the Securities Act of 1933.

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        The Registrant hereby amends this Registration Statement on such date or dates as may be necessary to delay its effective date until the Registrant shall file a further amendment which specifically states that this Registration Statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933 or until this Registration Statement shall become effective on such date as the Commission, acting pursuant to said Section 8(a), may determine.

EXPLANATORY NOTE

        This registration statement contains a base prospectus covering the offering, issuance and sale of the following securities of Alliant Energy Corporation, a Wisconsin corporation (the “Corporation”): (1) shares of its common stock; (2) its stock purchase contracts; and (3) its stock purchase units. The specific terms of the securities to be offered will be set forth in a prospectus supplement relating to such securities. In addition, this registration statement contains a form of prospectus supplement covering the offering, issuance and sale by the Corporation of up to 7,500,000 shares of common stock from time to time in privately negotiated transactions and/or any other method permitted by law, including sales deemed to be “at the market” offerings, pursuant to a sales agreement with Cantor Fitzgerald & Co.

The information in this prospectus supplement and accompanying prospectus is not complete and may be changed. We may not sell these securities until the registration statement filed with the Securities and Exchange Commission is effective. This prospectus supplement and accompanying prospectus are not an offer to sell these securities and they are not soliciting an offer to buy these securities in any state where this offer or sale is not permitted.

SUBJECT TO COMPLETION, DATED APRIL 9, 2004

Prospectus Supplement
(To Prospectus dated                     , 2004)

[ALLIANT ENERGY LOGO]

7,500,000 SHARES

ALLIANT ENERGY CORPORATION

COMMON STOCK

        This prospectus supplement relates to the issuance and sale of up to 7,500,000 shares of our common stock from time to time through our sales agent, Cantor Fitzgerald & Co. These sales, if any, will be made pursuant to the terms of the sales agreement between us and the sales agent, the form of which is an exhibit to the registration statement of which the accompanying prospectus is a part and is incorporated herein by reference.

        Our common stock trades on the New York Stock Exchange under the symbol “LNT.” Sales of shares of our common stock under this prospectus supplement, if any, may be made in privately negotiated transactions and/or any other method permitted by law, including sales deemed to be an “at the market” offering as defined in Rule 415 under the Securities Act, including sales made directly on the New York Stock Exchange, the existing trading market for our common stock, or sales made to or through a market maker other than on an exchange. We refer to these types of sales as at the market transactions. The sales agent will make all sales using commercially reasonable efforts consistent with its normal trading and sales practices, on mutually agreed terms between the sales agent and us. On April 8, 2004, the last reported sales price of our common stock on the New York Stock Exchange was $26.45 per share.

        The compensation to the sales agent for sales of common stock sold pursuant to the sales agreement will be 2.5% of the gross proceeds of the sales price per share for the first 3,250,000 shares sold and 2.0% of the gross proceeds of the sales price per share for any additional shares sold. The net proceeds from any sales under this prospectus supplement will be used as described under “Use of Proceeds” in the accompanying prospectus.

        In connection with the sale of common stock on our behalf, the sales agent may be deemed to be an “underwriter” within the meaning of the Securities Act, and the compensation of the sales agent may be deemed to be underwriting commissions or discounts. We have agreed to provide indemnification and contribution to the sales agent against certain liabilities, including liabilities under the Securities Act.

        You should read this prospectus supplement and the accompanying prospectus carefully before you invest. These documents contain information you should consider when making your investment decision.

Investing in the common stock involves risks that are described in the “Risk Factors” section beginning on page S-2 of this prospectus supplement.

        Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the accuracy or adequacy of this prospectus. Any representation to the contrary is a criminal offense.

[CANTOR FITZGERALD LOGO]

The date of this prospectus supplement is ____________, 2004.

RISK FACTORS

You should carefully consider the risk factors described below, as well as the other information included or incorporated by reference in this prospectus supplement and the accompanying prospectus, before making an investment in our common stock. The risks and uncertainties described below are not the only ones facing our company.

Risks related to the regulation of our business could impact the rates we are able to charge, our costs and our profitability.

        We are subject to comprehensive regulation by federal and state regulatory authorities, which significantly influences our operating environment and our ability to recover costs from our customers. In particular, we are regulated by state regulatory authorities with jurisdiction over public utilities, including the Iowa Utilities Board, the Public Service Commission of Wisconsin, the Illinois Commerce Commission and Minnesota Public Utilities Commission, the Securities and Exchange Commission under the Public Utility Holding Company Act of 1935 and by the Federal Energy Regulatory Commission. These authorities regulate many aspects of our operations, including, but not limited to: construction and maintenance of facilities; operations; safety; issuance of securities; accounting matters; transactions between affiliates; the rates that we can charge customers; the costs of fuel, purchased power and natural gas that we can recover from our customers; and the rate of return on capital that we are allowed to realize. Our ability to obtain rate adjustments to maintain our current rate of return depends upon regulatory action under applicable statutes and regulations, and we cannot assure you that we will be able to obtain rate adjustments or continue receiving our current authorized rates of return on equity capital. These regulatory authorities are also empowered to impose financial penalties and other sanctions on us if we are found to have violated statutes and regulations governing our utility operations. Our domestic utility business currently has several pending rate cases. If we do not receive the amount of rate relief that we expect, the increased rates are not approved on a timely basis or we are otherwise unable to recover our costs through rates, then we may experience an adverse impact on our results of operations, financial condition and cash flows. We are also subject to international rate regulation in the foreign markets in which we operate.

Our operating results may fluctuate on a seasonal and quarterly basis and can be adversely affected by milder weather.

        Our domestic electric and gas utility businesses are seasonal businesses and weather patterns can have a material impact on our operating performance. Demand for electricity is greater in the summer and winter months associated with cooling and heating. Because natural gas is heavily used for residential and commercial heating, the demand for this product depends significantly upon weather patterns in winter months. Accordingly, our operations have historically generated less revenues and income when weather conditions are milder in the winter and cooler in the summer. We expect that unusually mild winters and summers would have an adverse effect on our financial condition and results of operations.

A downgrade in our credit rating could negatively affect our borrowing costs and our ability to access capital and to operate our business.

        Our credit ratings may depend on, among other things, our earnings and cash flow outlooks for future periods and the success of our business plan. If either Standard & Poor’s Rating Services or Moody’s Investors Service were to downgrade our credit ratings, then our borrowing costs would increase, which would diminish our financial results, and our potential pool of investors and funding sources could decrease. In addition, some of our subsidiaries access debt and other capital from various sources and carry their own credit ratings. Any downgrade or other event negatively affecting the credit ratings of these subsidiaries could make their own costs of borrowing higher or access to funding sources more limited, which in turn could increase our need to provide liquidity in the form of capital contributions or loans to such subsidiaries, thus reducing the liquidity and borrowing availability of the consolidated group.

S-2

We depend on our continued access to capital markets.

        Some of our businesses, in particular our domestic utility business, rely on accessing the capital markets to support their capital expenditure programs and other capital requirements, including expenditures to build utility infrastructure and comply with future regulatory requirements. When necessary, we and our domestic utility subsidiaries secure funds from a variety of external sources, including the issuance of short-term debt, long-term debt securities, preferred stock or common stock, or the sale of accounts receivable. Fulfillment of our long-term strategies depends, at least in part, upon our ability and the ability of our subsidiaries to access capital at competitive rates and terms. If our or our subsidiaries’ access to capital were to become significantly constrained due to lowered credit ratings, prevailing market or industry conditions, regulatory constraints or other factors, then our results of operations and financial condition could be significantly adversely affected.

We have made substantial international investments, which may present additional risks to our business.

        As of December 31, 2003, we had $660 million in net investments in foreign countries, primarily in electric utility companies and generation facilities. International operations are subject to various risks, including political and economic instability, local labor market conditions, the impact of government regulations and taxation, differences in business practices and unusual weather patterns. In particular, we had $283 million of net investments in Brazil as of December 31, 2003, which was net of $162 million of pre-tax cumulative foreign currency translation losses. Our operations in Brazil have faced significant regulatory and political uncertainties and differences with local partners regarding business practices. Unfavorable changes in the international political, regulatory or business climate could have a material adverse effect on our growth plans for our international investments and, in turn, our results of operations, financial condition and cash flows. In addition, the results of operations and financial condition of our subsidiaries and investments that conduct operations in foreign countries are reported in the relevant foreign currencies and then translated into U.S. dollars at the applicable exchange rates for inclusion in our consolidated financial statements. Fluctuations between these currencies and the U.S. dollar may have a material adverse effect on our results of operations and financial condition and may also significantly affect the comparability of our results between financial periods. In addition, we have a $79 million loan receivable secured by a master planned resort community in Mexico. Repayment of the loan is contingent upon the developers complying with operating and development agreements and attaining projected lot sales. If the development of the project and related real estate sales are not successfully executed, we could incur material asset valuation charges.

As a holding company, we are subject to restrictions on our ability to pay dividends.

        We are a holding company with no significant operations of our own. Accordingly, the primary sources of funds for us to pay dividends to our shareowners are dividends and distributions our subsidiaries and investments pay to us. Our subsidiaries and investments are separate and distinct legal entities and have no obligation to pay any amounts to us, whether by dividends, loans or other payments. The ability of our subsidiaries and investments to pay dividends or make distributions to us and, accordingly, our ability to pay dividends on our common stock will depend on the earnings, cash flows, capital requirements and general financial condition of our subsidiaries and investments and on regulatory limitations. Our domestic utility subsidiaries each have dividend payment restrictions based on their respective bond indentures, the terms of their outstanding preferred stock and regulatory limitations applicable to them. If we do not receive adequate dividends and distributions from our subsidiaries and investments, then we may not be able to make or may have to reduce dividend payments on our common stock.

Failure to provide reliable service to our customers could adversely affect our operating results.

        Our utility businesses are obligated to provide safe and reliable service to their customers within their service territories. Meeting this commitment requires significant capital and other resources. Failure to provide safe and reliable service, including effects of equipment failures in electric and gas delivery systems, could adversely affect our operating results through reduced revenues and increased maintenance and capital costs. While we were not directly affected by the failure in the transmission grid that caused the power outage in a large portion of the northeastern United States and Canada in August 2003, the North American transmission grid is highly interconnected and, in extraordinary circumstances, disruptions at particular points within the grid could cause a systemic cascading response that could, in turn, result in an extensive power outage in our delivery systems. Power outages in our domestic utility business’ service territories could occur even if the disruptions originate outside of those territories.

S-3

The ongoing transformation of the energy industry could have a negative effect on our businesses.

        As a public utility holding company with significant utility assets, we conduct our utility operations in an ever-changing business environment. Electric energy generation, transmission and distribution are facing a period of significant change resulting from potential legislative, regulatory, economic and technological changes. These changes could impact competition in the electric wholesale and retail markets in the event customers of electric utilities are offered alternative suppliers. Such competitive pressures could result in our electric utilities losing customers and incurring stranded costs (i.e., assets and other costs rendered unrecoverable as the result of competitive pricing), which would be borne by our shareowners if we cannot recover the costs from customers. The Federal Energy Regulatory Commission regulates competition in the electric wholesale power generation market, and each state regulates whether to permit retail competition, the terms that would apply to such retail competition and the recovery of any portion of stranded costs that are ultimately determined to have resulted from retail competition. Although the pace of restructuring in our primary retail electric service territories has been delayed (and may continue to be delayed for a long period of time) due to uncertainty and developments in the industry, we cannot predict the timing of a restructured electric industry or the impact on our financial condition or results of operations.

Costs of compliance with new environmental laws and the incurrence of environmental liabilities could adversely affect our profitability.

        Our operations are subject to extensive regulation relating to environmental protection. New environmental laws and regulations affecting our operations may be adopted, and new interpretations of existing laws and regulations could be adopted or become applicable to us or our facilities, which may substantially increase environmental expenditures made by us in the future. We may not be able to recover all our costs for environmental expenditures related to our utility business through electric and natural gas rates in the future. Under current law, we may also be responsible for any on-site liabilities associated with the environmental condition of the facilities that we have previously owned or operated, regardless of whether the liabilities arose before, during or after the time we owned or operated the facilities. The incurrence of a material environmental liability could have a material adverse effect on our results of operations and financial condition.

Our domestic utility business may incur substantial costs and liabilities due to its interests in nuclear facilities.

        Our domestic utility subsidiaries own interests in two nuclear facilities. In November 2003, Wisconsin Power and Light Company, one of our domestic utility subsidiaries, signed a definitive agreement to sell its 41% ownership interest in the 545-megawatt Kewaunee Nuclear Power Plant. Pending regulatory approvals, the transaction is expected to be completed by the fall of 2004. Our ownership of interests in nuclear facilities involves risks, including: mechanical or structural problems; inadequacy or lapses in maintenance procedures; impairment of reactor operation and safety systems due to human error; costs of storage, handling and disposal of nuclear materials and the current lack of a long-term disposal solution for nuclear materials; limitations on the amounts and types of insurance coverage commercially available; and uncertainties regarding both technological and financial aspects of decommissioning nuclear facilities at the end of their licensed lives. The Nuclear Regulatory Commission, or NRC, has broad authority under federal law to impose licensing and safety-related requirements for the operation of nuclear generation facilities. In the event of non-compliance, the NRC has the authority to impose fines or shut down a unit, or both, depending upon its assessment of the severity of the situation, until compliance is achieved. Revised safety requirements approved by the NRC could necessitate substantial capital expenditures at our subsidiaries’ nuclear plants. In addition, although we have no reason to anticipate a serious nuclear incident, if an incident did occur, it could have a material adverse effect on our results of operations or financial condition. Furthermore, the non-compliance of other nuclear facilities operators with applicable regulations or the occurrence of a serious nuclear incident at other facilities could result in increased regulation of the industry as a whole, which could then increase our subsidiaries’ compliance costs and impact the results of operations of their facilities. We may not be able to recover all our costs related to our nuclear facilities through electric rates in the future.

S-4

Threats of terrorism and catastrophic events that could result from terrorism may impact our operations in unpredictable ways.

        We are subject to direct and indirect effects of terrorist threats and activities. Generation and transmission facilities, in general, have been identified as potential targets. In particular, nuclear generation facilities such as our two nuclear plants could be potential targets of terrorist activities. The effects of terrorist threats and activities include, among other things, terrorist actions or responses to such actions or threats, the inability to generate, purchase or transmit power, the risk of significant slowdown in growth or a decline in the U.S. economy, disruption or volatility in, or other effects on capital markets, and the increased cost and adequacy of security and insurance.

S-5

The information in this prospectus is not complete and may be changed. We may not sell these securities until the registration statement filed with the Securities and Exchange Commission is effective. This prospectus is not an offer to sell these securities and it is not soliciting an offer to buy these securities in any state where this offer or sale is not permitted.

PROSPECTUS

SUBJECT TO COMPLETION, DATED MARCH 31,APRIL 9, 2004

ALLIANT ENERGY CORPORATION
SHAREOWNER DIRECT PLANProspectus

6,000,000 Shares of Alliant Energy Corporation

$300,000,000 Aggregate Amount

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Alliant Energy Corporation

Common Stock

Stock Purchase Contracts

Stock Purchase Units

_________________

        We are offering participation in our Shareowner Direct Plan. The plan provides you with a varietyBy this prospectus, we may offer from time to time up to an aggregate of options, including:

        The plan provides that shares of our common stock may be purchased for participants from us or in the open market or in privately negotiated transactions. The price of shares of common stock purchased under the plan will be either:

No brokerage commissions, fees or service charges are charged tosecurities carefully before you in connection with purchases of shares under the plan or for participating in the plan.invest.

        Our common stock is listed on the New York Stock Exchange under the symbol “LNT.” The closing price of our common stock on March 30, 2004 on the New York Stock Exchange was $25.85 per share.

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        Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

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The date of this prospectus is ,____________, 2004.

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TABLE OF CONTENTS

ABOUT THIS PROSPECTUS

_________________        In this prospectus, “we,” “us” and “our” refer to Alliant Energy Corporation.

        This prospectus is part of a registration statement that we filed with the Securities and Exchange Commission, or SEC, utilizing a “shelf” registration process. Under this shelf process, we may, from time to time, sell the securities or combinations of the securities described in this prospectus in one or more offerings with a maximum aggregate offering price of up to $300,000,000. This prospectus provides you with a general description of the securities that we may offer. Each time we offer securities, we will provide a prospectus supplement that will contain specific information about the terms of that offering. The prospectus supplement may also add, update or change information contained in this prospectus. You should read both this prospectus and any prospectus supplement together with additional information described under the heading “Where You Can Find More Information.”

        We may use this prospectus to offer from time to time:

In this prospectus, we sometimes refer to the common stock, stock purchase contracts and stock purchase units collectively as the securities.

        You should rely only on the information contained or incorporated by reference in this prospectus.prospectus and in any supplement. We have not authorized any other person to provide you with different information. If anyone provides you with different or inconsistent information, you should not rely on it. We are not making an offer to sell these securities in any jurisdiction where the offer or sale is not permitted. You should assume that the information appearing in this prospectus and the documents incorporated by referenceaccompanying prospectus supplement is accurate only as of the date on their respective dates of those documents in which the information is contained.covers. Our business, financial condition, results orof operations and prospects may have changed since those dates.

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        Unless we otherwise indicate or unless the context requires otherwise, all references in this prospectus to “we,” “our,” “us” or similar references mean Alliant Energy Corporation.

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THE COMPANYALLIANT ENERGY CORPORATION

        We are an energy-services provider engaged primarily in public utility operations in both the Midwest and internationally. We also have significant non-regulated domestic and international operations. Through our subsidiaries and partners, we provide electric, natural gas, steam and water services, and various other energy-related products and services to more than three million customers worldwide. Our domestic utility business includes Interstate Power and Light Company and Wisconsin Power and Light Company, and is engaged principally in:

        The principal markets for our domestic utility business are located in Iowa, Wisconsin, Minnesota and Illinois.

        We are a registered public utility holding company subject to regulation by the Securities and Exchange CommissionSEC under the Public Utility Holding Company Act of 1935 and are subject to the regulatory provisions of that Act.

        Our principal executive offices are located at 4902 North Biltmore Lane, Madison, Wisconsin  53718, and our telephone number is (608) 458-3311.

USE OF PROCEEDS

        We have no basis for estimating eitherUnless otherwise specified in the number of authorized but unissued shares of common stock thatapplicable prospectus supplement, we will ultimately sell pursuant to the plan or the prices at which we will sell the shares. Any net proceeds we receive from the sale of shares under the plan will be added to our general funds and used for general corporate purposes. We will not receive any proceeds from the sale of shares under the plan that are acquired on the open market or in privately negotiated transactions.

SUMMARY OF PLAN FEATURES

        Some of the features of the plan, which are described in greater detail under “The Plan” below, are:

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THE PLAN

        The following are the terms and conditions of the plan.

Purpose

        The purpose of the plan is twofold. First, the plan provides our shareowners of record, other investors who choose to become shareowners of record and our employees and the employees of our subsidiaries with a simple, convenient and economical method to purchase shares of common stock and to reinvest all or a portion of their cash dividends in additional shares of common stock. Second, the plan provides us with the ability to sell our authorized but unissued shares of common stock to participants in the plan, which will raise funds to increase our equity base for general corporate purposes.

Plan Administration

        Through our Shareowner Services Department, the administrator of the plan, we administer the plan, keep records, send statements of account activity to participants and perform clerical and ministerial duties related to the plan. An independent agent, which is not an affiliate of ours, designated by the administrator will make purchases and sales of shares of common stock for the plan in the open market or in privately negotiated transactions. Subject to applicable securities laws and some limitations, the independent agent will have full discretion as to the timing of, and all matters relating to, purchases and sales of shares of common stock for the plan other than for the purchase from us of authorized but unissued shares.

        The administrator will establish and maintain a separate account under the plan for each participant. We will credit to your account all shares of common stock, including any fractional shares, computed to four decimal places, purchased for a participant under the plan, and any shares a participant deposits through the plan’s share safekeeping service.

        You should direct all inquiries and instructions concerning the plan to:

        All correspondence should include your shareowner account number, taxpayer identification or social security number and daytime telephone number where you may be contacted during normal working hours to facilitate a prompt response.

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Enrollment Procedures

Shareowners

        If you are currently a shareowner of record, then you may enroll in the plan at any time by completing and returning an authorization form to the administrator. You should direct requests for authorization forms to the administrator, either by telephone, in writing or through the internet.

“Street Name” Holders

        If you own shares of common stock that are held on your behalf by a bank, broker, trustee or other agent, then you may enroll in the plan by registering one or more shares of common stock directly in your name and by returning a completed authorization form to the administrator. See “Transfer of Shares from Street Name.”

Non-Shareowners

        With limited exceptions described below, if you are not currently a shareowner of record, then you may enroll in the plan by completing and returning an authorization form to the administrator together with an initial investment of at least $250, but not more than $120,000, or by authorizing automatic monthly withdrawals (“automatic investments”) of at least $25, in either case which will be used to purchase shares of common stock for your plan account. See “Initial Investments and Optional Cash Investments” and “Methods of Investment.”

Employees

        With limited exceptions described below, any of our employees or employees of our subsidiaries may enroll in the plan at any time by completing and returning an authorization form to the administrator or by enrolling in the same manner as any other eligible investor described above.

Exceptions

        We reserve the right to prohibit participation in the plan by non-shareowners who reside in a state where participation in the plan by non-shareowners who reside in the state would require us to take special action under the securities or “blue sky” laws of the state and we have not yet taken the required action. We also reserve the right to prohibit participation in the plan by any investor, whether or not a holder of record of shares of common stock, who is a citizen or resident of a country other than the United States, if his or her participation would violate local laws and regulations applicable to us or the prospective participant. In any such case, the administrator will return any authorization form and initial investment tendered by any non-shareowner who resides in such state or country.

General

        We will process authorization forms as promptly as practicable. Participation in the plan will begin after the administrator has reviewed and accepted a properly completed form.

Transfer of Shares From Street Name

        If you are a beneficial owner of common stock whose shares are registered in the name of a bank, broker, trustee or other agent, then you may participate in the plan with respect to these shares by either:

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Initial Investments and Optional Cash Investments

        If you are not currently a shareowner of record, then you must make an initial investment of at least $250, but not more than $120,000, in the form of a personal check or money order, automatic investment of at least $25 or, for employees, payroll deduction of at least the amount specified on the payroll withholding form, and you must include your initial investment with the completed authorization form you return to the administrator. See “Methods of Investment.”

        Once you are enrolled in the plan, you may purchase additional shares of common stock using the plan’s optional cash investment feature. You must make optional cash investments in amounts of not less than $25 per investment and may not aggregate more than $120,000 per calendar year, including any initial investment, whether by check or automatic investment. We will not waive these restrictions; however, the $25 minimum is not applicable to employee participants who make investments through payroll deductions. You have no obligation to make an optional cash investment at any time, and the amount of your investments may vary from time to time.

        The administrator must receive authorization forms, which are subject to our review, with initial investments at least five business days prior to the next investment date (as defined under “Purchase of Common Stock”). The administrator will invest initial investments and optional cash investments on the next investment date, provided the administrator receives such investments at least five business days prior to that investment date.

        We will not pay interest on any initial investments or optional cash investments received and held for investment under the plan. Therefore, it is to your benefit to mail an initial investment or an optional cash investment so that the administrator receives it shortly, but not less than five business days, before an investment date. To receive dividends, the administrator must have received and invested an initial investment or an optional cash investment on the investment date prior to the dividend record date.

        Upon written request, we will refund your initial investment or any optional cash investment, provided we receive your request at least two business days prior to the investment date following receipt of your investment. However, we will not make a refund until we actually receive the funds.

Methods of Investment

        Your total annual investment cannot exceed $120,000 per calendar year and must be made in U.S. dollars. For the purpose of applying this limit, all investments during any calendar year, including initial and optional cash investments, but excluding dividend reinvestments and deposits of shares in the plan’s share safekeeping service, are aggregated. We will not pay any interest on amounts we hold pending investment.

Check Investment

        You may make initial investments and optional cash investments by personal check or money order payable to “Alliant Energy.” Initial investments are subject to our collection for the full face value in U.S. funds.

        If a check is returned unpaid for any reason, then we will consider the request for investment of these funds null and void. If any shares have been purchased with these funds, then the administrator will be entitled to remove those shares from the participant’s account and sell those shares to satisfy the balance of the uncollected funds. Ifuse the net proceeds from the sale are insufficientof the securities to cover this balance, thenmake capital contributions to our domestic utility business, which may use these capital contributions for financing the development and construction of new generation and distribution facilities, funding additional working capital, financing capital expenditures and other general corporate purposes; to make capital contributions to our domestic non-regulated generation business, which would use these capital contributions for financing the development and construction of new generation facilities intended to serve the growing electricity demand of our domestic utility business; or to repay debt. Until we will, in addition to any other rightsuse the net proceeds from the sale of the securities for these purposes, we may have, be entitledplace the net proceeds in temporary investments.

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DESCRIPTION OF COMMON STOCK

        The following description of our common stock summarizes general terms and provisions that apply to sell any additional shares from your accountthe common stock. Since this is only a summary it does not contain all of the information that may be necessaryimportant to satisfy the uncollected balance.

Automatic Investment

        You may make automatic monthly investments, whether initial or optional cash investments,you. The summary is subject to and qualified in its entirety by reference to our articles of at least $25 by electronic funds transfer from a predesignated account with a U.S. financial institution. To initiate automatic investments, you must completeincorporation and returnour rights agreement, which are filed as exhibits to the administrator an automatic investment formregistration statement of which this prospectus is a part and an authorization form, as well as deliverincorporated by reference into this prospectus. See “Where You Can Find More Information.”

General

        Our articles of incorporation provide that we have authority to issue 200,000,000 shares of common stock. We have submitted to our shareowners a proposal to increase our authorized shares to 240,000,000 at our annual meeting of shareowners on May 21, 2004. The SEC has authorized us under the administrator a voided blank check or a savings deposit slip forPublic Utility Company Act of 1935 to issue the account from which funds areshares to be drawn. You may obtain automatic investment forms fromoffered pursuant to this prospectus. We do not have the administrator. Automatic investments will be initiated as promptly as practicable. Funds then will be drawn from your designated account onauthority under our articles of incorporation to issue shares of preferred stock.

Common Stock

        All of the tenth dayissued and outstanding shares of each month, or, if the tenth day falls on a weekend or bank holiday, the first business day thereafter, and will be invested inour common stock on the next investment date.

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        You may change the amount of your future automatic investments by completingare fully paid and submitting to the administrator a new automatic investment form. You may terminate your automatic investments by notifying the administrator by phone, in writing or through the internet. To be effective with respect to the next automatic investment date, the administrator must receive the new form or notice at least six business days preceding that date.

        Electronic direct deposit of cash dividends that you elect to receive also is available through the plan.

Payroll Deductions

        Our employees or employees of our subsidiaries may also make investments, whether initial or optional cash investments, by means of payroll deduction,nonassessable, and the $250 and $25 minimums for initial investment and optional cash investments, respectively, will not apply to investments made through payroll deductions. To initiate payroll deductions, the employee must complete and return to the administrator a payroll withholding form and an authorization form.

        The payroll withholding form, which allows participating employees to decide the dollar amount to be deducted from their paychecks for each pay period, will become effective as promptly as practicable. Deductions will be used to purchase full and fractional, computed to four decimal places, shares of common stock onto be sold by us, upon completion of any offering, will be fully paid and nonassessable, except in either case as provided under Section 180.0622(2)(b) of the next investment date. The minimum deduction per pay period is the amount specified on the payroll withholding form.

        Payroll deduction authorizationsWisconsin Business Corporation Law. This provision of Wisconsin law provides that shareowners will remain in effect until cancelled or modified by the employee, which a participating employee may accomplish by completing and returning a new payroll withholding form indicating the change desired. To be effective with respectpersonally liable up to the next payroll deduction,par value of the administrator must receiveshares owned by them for all debts we owe to our employees for services performed for our company not exceeding six months service in any one case. A Wisconsin trial court has interpreted “par value” to mean the new payroll withholding form at least six business days preceding that date.

Dividend Reinvestment Options

        The authorization form allows you to choose a reinvestment option for participation in the plan. If you do not specify otherwise, then your account will be enrolled for full dividend reinvestment. By choosing the appropriate box, you may select:

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        If you participate in the plan’s full or partial dividend reinvestment option, then reinvestment will commence with the first dividend payable after the dividend record date following your enrollment. We will publicly announce dividend record dates.

        If you wish to change your method of participation, then you must obtain and complete a new authorization form and send it to the administrator. To be effective with respect to a particular common stock dividend, the administrator must receive the new authorization form at least two business days before the record date for the dividend. If you elect to ceaseshares rather than the reinvestment of your dividends, then you may receive themlower stated par value. While the Wisconsin Supreme Court by check or electronic direct deposit. You may also continue to havean evenly divided vote affirmed the administrator hold your shares through the share safekeeping service, buy shares with optional cash investments, and sell or transfer the shares as you desire. See “Share Safekeeping,” “Initial Investments and Optional Cash Investments,” “Sale of Common Stock” and “Gift/Transfer of Shares Held in the Plan.”

        On each applicable investment date, we will promptly, after deducting withholding taxes, if any, combine and pay over to the administrator all cash dividends payable on shares held by the administrator for all participants who are reinvesting their dividends in the plan. The administrator will apply the dividends to the purchase of shares of common stock. The administrator will credit the proportionate number of shares, computed to four decimal places, purchased by the administrator to your account.

Purchase of Common Stock

        Reinvested common stock dividends, initial investments, optional cash investments and proceeds, which will be treated regardlesstrial court’s decision, that affirmation technically provides no precedential effect because of the amount as optional cash purchases, from the sale or redemption of common stock subscription or other rights, if any, received by the administrator on behalf of participants will be used to acquire either outstanding shares of common stock or authorized but unissued shares of common stock from us, provided that we are willing to sell the common stock. Purchases of outstanding shares of common stock on behalf of plan participants may be made on any stock exchange in the U.S. where ourcourt’s even decision.

        Our common stock is traded, in the over-the-counter market or by privately negotiated transactions on terms that the independent agent for the administratorentitled to such dividends as our board of directors may reasonably determine at thedeclare from time of purchase. Any shares purchased from us will be madeto time in accordance with applicable requirements.

        The administrator and its designated independent agent may combine your funds with those of other participants for the purpose of purchasing shares. Neither we nor any affiliated purchasers will exercise any direct or indirect control or influence over the times when, or prices at which, the designated independent agent may purchase common stock for the plan or the amount of shares the designated independent agent may purchase.

        Purchases of shares of common stock under the plan will be made on or about the following applicable “investment dates”:

        Purchases may be made over a period of several days in the case of open market purchases. All open market purchases will be aggregated for the investment date.

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        Fordependent upon a number of reasons,factors, including observancethe ability of our subsidiaries to pay dividends. Our utility subsidiaries each have restrictions on the rules and regulationspayment of the Securities and Exchange Commission or other regulatory agencies requiring temporary curtailment or suspension of purchases, the investment of all or part of the funds available in your account may be delayed from time to time. We will not pay any interestdividends on funds we hold pending investment. However, shares oftheir common stock will either be purchased within 35 daysbased on their respective bond indentures, the terms of receipt of initial investments or optional cash investments or funds will be returnedtheir outstanding preferred stock and regulatory restrictions applicable to you.them.

        We will credit your account with that number of shares of common stock, including any fractional shares, computed to four decimal places, equal to the total amount to be invested divided by the applicable purchase price per share.

Price to Participants

        The price of newly-issued shares of common stock purchased from us for participants will be the average, computed to four decimal places, of the high and low sale prices of shares of common stock as reported on the New York Stock Exchange on the applicable investment date. If no trading occurs on the New York Stock Exchange in the common stock on the applicable investment date, then the price will be determined with reference to the next preceding date on which the common stock is traded on the New York Stock Exchange. The price of shares of common stock purchased for participants on the open market or in privately negotiated transactions will be the weighted average price of all the shares purchased for the applicable investment date. If an investment under the plan is at any time made in both newly-issued and already outstanding shares, then the shares purchased will be allocated as proportionately as is practicable among the accounts of all participants for whom funds are being invested at that time.

        Under the plan, you do not have the ability to order the purchase of a specific number of shares, purchase of shares at a specified price or a particular date of purchase, as could be done with respect to purchases through a broker.

Sale of Common Stock

        You can sell all or part of your shares held in your plan account by providing the administrator with written instructions, signed by all registered holders. You cannot sell any certificated shares that you may be holding unless you first deposit them with the administrator pursuant to the plan’s share safekeeping service.

        Your sales will be made as soon as practicable after the administrator receives written instructions from you. Requests to sell plan shares will be aggregated and processed within ten business days by an independent broker, which is not an affiliate of ours, designated by the administrator on the open market at prevailing market prices. When you sell your shares, the price per share that you will receive will be the average of the proceeds from all shares sold by the administrator, less your proportionate share of the brokerage commission, transfer taxes, if any, and withholding tax, if any.

        You are required to maintain a balance of one or more full shares of common stock or we may terminate your plan account. We will treat a request to sell all shares held in your account as a withdrawal from the plan. See “Our Termination of an Account” and “Withdrawal and Termination.”

Custody of Stock and Issuance of Stock Certificates

        The administrator will hold all shares purchased on your behalf through the plan in safekeeping in our name or the name of our nominee. However, you may at any time and without charge, obtain a certificate for all or part of the whole shares credited to your plan account by making a request in writing to the administrator. We will not issue any certificates for fractional shares. Obtaining certificates for your plan account shares in no way affects dividend reinvestment. See “Dividend Reinvestment Options.”

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Share Safekeeping

        The plan’s “share safekeeping” service allows you to deposit common stock certificates held by you with the administrator for safekeeping. The advantages of the share safekeeping service are:

        To participate in the plan’s share safekeeping service, you must complete and return an authorization form, along with the common stock certificates you wish to deposit, to the administrator by registered and insured mail. You should not endorse the certificates or complete the assignment section. You may obtain an authorization form by calling or writing the administrator. If you have lost any of your certificates, then you must replace them before you may participate in the share safekeeping service.

Gift/Transfer of Shares Held in the Plan

        You may transfer the ownership of some or all of your plan shares, including shares held in safekeeping, by mailing to the administrator a properly executed stock assignment form, which you may obtain from the administrator or a financial institution, with a Medallion Signature Guarantee for all owners and a letter of instruction. A Medallion Signature Guarantee is a signature guarantee by an institution such as a commercial bank, trust company, securities broker/dealer, credit union or a saving institution participating in a Medallion Program approved by the Securities Transfer Association, Inc. You may transfer shares to new or existing shareowners.

        Unless otherwise instructed, the administrator will retain the shares and enroll the transferee in full dividend reinvestment, provided the transferee is eligible to participate. The new participant will receive a statement showing the number of shares transferred and now held in his or her plan account, which will be considered the transaction confirmation.

Withdrawal and Termination

        You may withdraw from the plan at any time by giving written notice to the administrator. If you terminate participation in the plan, all reinvestment of your dividends will immediately stop if the notice of withdrawal is received by the administrator not later than ten business days prior to the record date for the next dividend payment. Investment of optional cash will stop immediately if notification of withdrawal from the plan is received by the administrator at least two business days prior to the applicable investment date. The entire amount of any optional cash received for which investment has been stopped by termination of participation in the plan will be refunded to you without interest.

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        Upon withdrawal from the plan, you or your personal representative or other authorized agent may elect to either receive a certificate for the number of whole shares held in your account and a check for the value of any fractional share, or sell all shares in your account as described under “Sale of Common Stock.”

        If you terminate participation in the plan, then you will receive a check for the cash value of any fractional share held in your plan accounts. Fractions of shares will be valued at the then current market price, determined in the same manner as provided with respect to the sale of whole shares, less brokerage commissions, transfer taxes and withholding taxes, if any.

        You may not make any optional cash investments after you have terminated participation in the plan unless and until you rejoin the plan, which you may accomplish by complying with the enrollment procedures. See “Enrollment Procedures.” However, we reserve the right to reject any authorization form from a previous participant on grounds of excessive joining and termination. Such reservation is intended to minimize administrative expense and to encourage use of the plan as a long-term investment service.

Stock Splits, Stock Dividends and Rights Offerings

        We will credit to your account any shares distributed pursuant to stock dividends or stock splits effected by us on shares held by the administrator for you. If we make available toOnly holders of our common stock subscription orwill be entitled to vote for the election of members to our board of directors and on all other matters. Holders of our common stock are entitled to one vote per share of common stock held by them on all matters properly submitted to a vote of shareowners, subject to Section 180.1150 of the Wisconsin Business Corporation Law. See “– Statutory Provisions.” Shareowners have no cumulative voting rights, which means that the holders of shares entitled to purchase additionalexercise more than 50% of the voting power are able to elect all of the directors to be elected. Our board of directors is divided into three classes, with staggered terms of three years each.

        All shares of common stock or other securities, then the administrator will, if and when the rights trade independently, sell the rights accruingare entitled to all shares held by the administrator for the participants and will apply the net proceeds of the sale to the purchase of common stock. However, we will,participate equally in advance of a subscription offer, or, if the rights may not be independently traded upon issuance, prior to the date on which the rights trade independently, inform you that if you do not want the administrator to sell your rights and invest the proceeds, then it will be necessary for you to transfer all full shares held under the plan to your own name by a given date. This would permit you to exercise, transfer or sell the rights on the shares. If rights issued by us are redeemed prior to the date that the rights trade independently, then the administrator will invest the resultant fundsdistributions in additional shares of common stock.

Voting Rights

        The administrator will vote at shareowners’ meetings any full sharesliquidation. Holders of common stock creditedhave no preemptive rights to your account under the plan in accordance with your instructions.subscribe for or purchase our shares. There are no conversion rights, sinking fund or redemption provisions applicable to our common stock.

        The administrator will not vote such shares if you do not give any instructions. A proxy card will be mailed to you representing the shares oftransfer agent for our common stock held in your plan account.is our Shareowner Services Department.

Statements and Reports

        You will receive quarterly statements showing all transactions in your account for that quarter, including the amount invested, the price paid per share, the number of shares purchased and total shares accumulated. You should retain these statements for purposes of establishing the cost basis of shares purchased under the plan for income tax and other purposes.

        The administrator will also send you an account statement as soon as practicable after each initial investment, optional cash investment, sale or transfer.

        In addition, you will receive copies of the same communications we send to all other holders of common stock, including our annual reports, notices of annual meetings and proxy statements, and information you need for reporting dividend income for Federal income tax purposes.

        All notices, statements and reports to you will be addressed to you at your last address we have on record. Therefore, you must promptly notify us by phone, in writing or through the internet of any change of address.

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No Right to Draw Against Account

        You will not have a right to draw checks or drafts against your account or give instructions to the administrator with respect to any shares or cash held therein, except as expressly provided in this prospectus.

Duties and Responsibilities

        Neither we nor any of our agents will have any responsibility beyond the exercise of ordinary care for any action taken or omitted pursuant to the plan, nor will we have any duties, responsibilities or liabilities, except as expressly set forth in this prospectus. Neither we nor any of our agents will be liable under the plan for any act done in good faith or for any good faith omission to act, including any claims of liability with respect to the prices at which shares are purchased or sold for your account, the times when the purchases or sales are made or any inability to purchase or sell shares, for any fluctuation in the market value after purchase or sale of shares, or arising out of failure to terminate your account upon your death prior to receipt of notice in writing of your death.

        You should recognize that we cannot provide any assurance of profit or protection against loss on any shares purchased under the plan.

Change or Termination of the Plan

        We reserve the right to amend, modify, suspend or terminate the plan in whole, in part, or with respect to participants in one or more jurisdictions. We will send notice of any suspension, termination or significant amendment, or modification of the plan to all affected participants. No such event will affect any shares then credited to a participant’s account. Upon any whole or partial termination of the plan by us, a certificate for whole shares credited to an affected participant’s account under the plan will be issued to the participant and a cash payment will be made for any fraction of a share. Fractions of shares will be valued at the then current market price, determined in the same manner as provided with respect to the sale of whole shares, less brokerage commissions, transfer taxes and withholding tax, if any. Any uninvested funds held by the administrator at the time of any suspension or termination of the plan will be remitted by the administrator to affected participants.

Our Termination of an Account

        We may terminate your enrollment in the plan if you no longer hold any shares of record and your plan shares total less than one whole share of common stock. At our discretion we may also terminate your participation in the plan upon written notice mailed to you at the address appearing on our records. Upon termination, you will receive a certificate for whole shares held in your account and a check for the value of any fractional share held in your plan account. Fractions of shares will be valued at the then current market price, determined in the same manner as provided with respect to the sale of whole shares, less brokerage commissions, transfer taxes and withholding tax, if any.

Interpretation of the Plan

        We may in our discretion interpret and regulate the plan as we deem necessary or desirable in connection with the operation of the plan and resolve questions or ambiguities concerning the various provisions of the plan.

Governing Law

        The plan will be governed by the internal laws of the State of Wisconsin.

FEDERAL INCOME TAX CONSEQUENCES

The following discussion sets forth the general Federal income tax consequences for an individual participating in the plan. This discussion is not, however, intended to be an exhaustive treatment of the tax consequences. Future legislative changes or changes in administrative or judicial interpretation, some or all of which may be retroactive, could significantly alter the tax treatment discussed herein. Accordingly, and because tax consequences may differ among participants in the plan, you should consult your own tax advisor to determine the particular tax consequences, including state income tax consequences, that may result from participation in and the subsequent disposal of shares purchased under the plan.

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General Considerations

        In general, participants reinvesting dividends under the plan have the same federal income tax consequences with respect to their dividends as do shareowners who are not reinvesting dividends under the plan. On the dividend payment date, participants will receive a taxable dividend equal to the cash dividend reinvested, to the extent we have earnings and profits. This treatment applies with respect to both the shares of common stock held of record by the participant and the participant’s plan account shares even though the dividend amount is not actually received in cash but is instead applied to the purchase of shares of common stock for the participant’s plan account. If shares are purchased on the open market or in a privately negotiated transaction, then the participant’s share of brokerage fees, if any, that we pay will also be taxed as an additional dividend to that participant, to the extent we have earnings and profits.

        Shares or any fractions of shares of common stock purchased on the open market or in a privately negotiated transaction with reinvested dividends will have a tax basis equal to the amount paid therefor, increased by any brokerage fees treated as a dividend to the participant. Shares or any fractions of shares of common stock purchased from us with reinvested dividends will have a tax basis equal to the amount of the dividend. Whether purchased on the open market or in a privately negotiated transaction or from us, the shares or any fractions of shares will have a holding period beginning on the day following the purchase date.

        Participants that make initial or optional cash investments under the plan will be deemed to have received an additional taxable dividend in the amount of the participant’s pro rata share of the brokerage commissions, if any, that we pay, to the extent we have earnings and profits. Such brokerage commissions will only be incurred on the purchase of the common stock in the open market or in privately negotiated transactions. Shares or any fractions of shares purchased with initial or optional cash investments will have a tax basis equal to the amount of the payments increased by the amount of brokerage fees, if any, treated as a taxable dividend to the participant with respect to those shares or fractions of shares. The holding period for the shares or fractions of shares will begin on the day following the purchase date.

        Participants should not be treated as receiving an additional taxable dividend based upon their pro rata share of the costs of administering the plan which we pay. However, we cannot provide any assurances that the Internal Revenue Service will agree with this position. We have no present plans to seek formal advice from the IRS on this issue.

        Participants will not recognize taxable income when they receive certificates for whole shares credited to their account, either upon their request for the certificates or upon withdrawal from, or termination of the plan. However, participants will generally recognize gain or loss when shares acquired under the plan are sold or exchanged either through the plan at their request or by participants themselves after receipt of certificates for shares from the plan. Participants will also generally recognize gain or loss when they receive cash payments for fractional shares credited to their accounts, upon the sale of shares through the plan or upon withdrawal from or termination of the plan. The amount of gain or loss is the difference between the amount which the participant receives for his or her whole shares or fractional shares and the tax basis thereof. Provided that the shares are capital assets in the hands of the participant, the gain or loss will be a capital gain or loss, long-term or short-term depending on the participant’s holding period.

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Tax Withholding

        In the case of a participating foreign shareowner whose dividends are subject to United States income tax withholding, or a participating domestic shareowner subject to backup withholding because a correct taxpayer identification number has not been furnished or otherwise, the tax required to be withheld will be deducted from the amount of any cash dividend reinvested. Since any withholding tax applies also to a dividend on shares credited to the participant’s plan account, only the net dividend on the shares will be applied to the purchase of additional shares of common stock. The regular statements sent to participants will indicate the amount of tax withheld. Likewise, participants selling shares through the plan who are subject to backup or other withholding will receive only the net cash proceeds from the sale as required by the Internal Revenue Code and the Treasury Regulations thereunder. We cannot refund amounts withheld. Participants subject to withholding should contact their tax advisors or the IRS for additional information.

RIGHTS TO PURCHASE COMMON STOCKCommon Share Purchase Rights

        We have entered into a rights agreement pursuant to which each outstanding share of our common stock, including those shares that we are sellingbeing sold by us pursuant to this prospectus, has attached a right to purchase one-half of one share of our common stock. A right will also attach to each share of our common stock that we subsequently issue prior to the expiration of the rights agreement. Under circumstances described below, the rights will entitle the holder of the rights to purchase additional shares of our common stock. In this prospectus and any accompanying prospectus supplement, unless the context requires otherwise, all references to our common stock include the accompanying rights.

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        Currently, the rights are not exercisable and trade with ourthe common stock. If the rights become exercisable, then each full right, unless held by a person or group that beneficially owns more than 15% of our outstanding common stock, will initially entitle the holder to purchase one half of one share of our common stock at a purchase price of $95 per full share, or $47.50 per half share, subject to adjustment. The rights will become exercisable only if a person or group has acquired, or announced an intention to acquire, 15% or more of our outstanding common stock. Under some circumstances, including the existence of a 15% acquiring party, each holder of a right, other than the acquiring party, will be entitled to purchase at the right’s then-current exercise price, shares of our common stock having a market value of two times the exercise price. If another corporation acquires us after a party acquires 15% or more of our common stock, then each holder of a right will be entitled to receive the acquiring corporation’s common shares having a market value of two times the exercise price. The rights may be redeemed at a price of $0.001 per right until a party acquires 15% or more of our common stock and, after that time, may be exchanged for one share of our common stock per right until a party acquires 50% or more of our common stock. The rights expire on January 20, 2009, subject to extension. Under the rights agreement, our board of directors may reduce the thresholds applicable to the rights from 15% to not less than 10%. The rights do not have voting or dividend rights and, until they become exercisable, have no dilutive effect on our earnings.

Statutory Provisions

        Because we are a public utility holding company under the Public Utility Holding Company Act of 1935, the SEC must approve the acquisition of any of our securities or utility assets by a registered public utility holding company or any person who would, as a result of such acquisition, become an affiliate of two or more public utility companies. Similarly, Section 196.795(3) of the Wisconsin Statutes provides that no person may hold or acquire, directly or indirectly, more than 10% of the outstanding securities of a public utility holding company such as us without the approval of the Public Service Commission of Wisconsin.

        Section 180.1150 of the Wisconsin Business Corporation Law provides that the voting power of public Wisconsin corporations such as us held by any person or persons acting as a group in excess of 20% of the company’s voting power is limited to 10% of the full voting power of those shares, unless full voting power of those shares has been restored pursuant to a vote of shareowners. Sections 180.1140 to 180.1144 of the Wisconsin Business Corporation Law contain some limitations and special voting provisions applicable to specified business combinations involving Wisconsin corporations such as us and a significant shareholder, unless the board of directors of the corporation approves the business combination or the shareholder’s acquisition of shares before these shares are acquired.

        Similarly, Sections 180.1130 to 180.1133 of the Wisconsin Business Corporation Law contain special voting provisions applicable to some business combinations, unless specified minimum price and procedural requirements are met. Following commencement of a takeover offer, Section 180.1134 of the Wisconsin Business Corporation Law imposes special voting requirements on share repurchases effected at a premium to the market and on asset sales by the corporation, unless, as it relates to the potential sale of assets, the corporation has at least three independent directors and a majority of the independent directors vote not to have the provision apply to the corporation.

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DESCRIPTION OF STOCK PURCHASE CONTRACTS
AND STOCK PURCHASE UNITS

        We may issue stock purchase contracts, including contracts that obligate holders to purchase from us, and us to sell to these holders, a specified number of shares of common stock at a future date or dates. The price per share of common stock may be fixed at the time the stock purchase contracts are issued or may be determined by reference to a specific formula set forth in the stock purchase contracts.

        The stock purchase contracts may be issued separately or as a part of stock purchase units. Stock purchase units consist of a stock purchase contract and either debt securities of our subsidiaries or debt obligations of third parties, including U.S. Treasury securities, securing the holders’ obligations to purchase the common stock under the stock purchase contracts.

        The stock purchase contracts may require us to make periodic payments to the holders of some or all of the stock purchase units or vice versa, and such payments may be unsecured or prefunded on some basis. The stock purchase contracts may require holders to secure their obligations under these stock purchase contracts in a specified manner.

        A prospectus supplement will describe the terms of any stock purchase contracts or stock purchase units being offered. The description in the prospectus supplement will not necessarily be complete, and you should read the stock purchase contracts and, if applicable, collateral or depositary arrangements, relating to the stock purchase contracts or stock purchase units. Material U.S. federal income tax considerations applicable to the stock purchase units and stock purchase contracts will be discussed in the related prospectus supplement.

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PLAN OF DISTRIBUTION

        We may sell the securities in one or more of the following ways from time to time:

        The applicable prospectus supplement will set forth the terms of the offering of securities, including the name or names of any underwriters, dealers or agents, the purchase price of the securities and the proceeds to us from the sale, any underwriting discounts or agency fees and other items constituting underwriters’ or agents’ compensation and any discounts or concessions allowed or reallowed or paid to dealers.

        If underwriters are utilized in the sale, the securities will be acquired by the underwriters for their own account pursuant to an underwriting agreement that we will execute with the underwriters at the time an agreement for such sale is reached. Such securities may be resold from time to time in one or more transactions, including negotiated transactions, at a fixed public offering price or prices, which may be changed, or at market or varying prices determined at the time of sale. The securities may be either offered to the public through underwriting syndicates represented by managing underwriters or by underwriters without a syndicate. Generally, the obligations of the underwriters to purchase securities will be subject to conditions precedent and the underwriters will be obligated to purchase all of the securities if any are purchased. Any public offering price and any discounts or concessions allowed or reallowed or paid to dealers may be changed from time to time.

        We may engage Cantor Fitzgerald & Co. to act as underwriter for an offering from time to time of our common stock in one or more placements. If we reach agreement with Cantor on a placement, including the number of shares of common stock to be offered in the placement and any minimum price below which sales may not be made, Cantor would agree to use its commercially reasonable efforts, consistent with its normal trading and sales practices, to try to sell such shares on such terms. Cantor could make sales in privately negotiated transactions and/or any other method permitted by law, including sales deemed to be an “at the market” offering as defined in Rule 415 under the Securities Act, including sales made directly on the New York Stock Exchange, the existing trading market for our common stock, or sales made to or through a market maker other than on an exchange. At the market offerings may not exceed 10% of the aggregate market value of our outstanding voting securities held by non-affiliates on a date within 60 days prior to the filing of the registration statement of which this prospectus is a part.

        If dealers are utilized in the sale of the securities, we will sell the securities to the dealers, as principals. The dealers may then resell the securities to the public at varying prices to be determined by the dealers at the time of resale.

        We may sell securities directly or through agents we designate from time to time. Generally, any agent will be acting on a best efforts basis for the period of its appointment.

        The securities may also be offered and sold, if so indicated in the applicable prospectus supplement, in connection with a remarketing upon their purchase, in accordance with a redemption or repayment pursuant to their terms, or otherwise, by one or more remarketing firms, acting as principals for their own accounts or as agents for us. Any remarketing firm will be identified and the terms of its agreements, if any, with us and its compensation will be described in the applicable prospectus supplement.

        Underwriters, agents and dealers may be entitled under agreements entered into with us to be indemnified against civil liabilities, including liabilities under the Securities Act of 1933, or to contribution with respect to payments that the underwriters or agents may be required to make in respect thereof. Underwriters, agents and dealers may be customers of, engage in transactions with, or perform services for us and our subsidiaries and affiliates in the ordinary course of business.

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WHERE YOU CAN FIND MORE INFORMATION

        We file annual, quarterly and current reports, proxy statements and other information with the SEC. We also filed a registration statement on Form S-3, including exhibits, under the Securities Act of 1933 with respect to the securities offered by this prospectus. This prospectus is a part of the registration statement, but does not contain all of the information included in the registration statement or the exhibits. You may read and copy the registration statement and any other document that we file at the SEC’s public reference room at 450 Fifth Street, N.W., Washington D.C. You can call the SEC at 1-800-SEC-0330 for further information on the operation of the public reference room. You can also find our public filings with the SEC on the internet at a web site maintained by the SEC located at http://www.sec.gov.

        We are “incorporating by reference” specified documents that we file with the SEC, which means:

        We incorporate by reference the documents listed below and any future filings we make with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Securities Exchange Act of 1934 after the date of this prospectus and before the end of the offering of the securities pursuant to this prospectus:

Some of these reports, however, are or may be filed on a combined basis with our direct subsidiaries, Interstate Power and Light Company and Wisconsin Power and Light Company. Information contained in these reports relating to these entities is filed by them on their own behalf and not by us.

        You may request a copy of any of these filings, at no cost, by writing to F. J. Buri, Corporate Secretary, Alliant Energy Corporation, 4902 North Biltmore Lane, Madison, Wisconsin 53718, or by calling Mr. Buri at (608) 458-3311.

LEGAL MATTERS

        The validity of the shares of common stocksecurities offered by this prospectus will be passed upon for us by Foley & Lardner LLP, Milwaukee, Wisconsin.LLP.

EXPERTS

        The consolidated financial statements and the related financial statement schedule incorporated in this prospectus by reference tofrom Alliant Energy Corporation’s Annual Report on Form 10-K for the year ended December 31, 2003 have been audited by Deloitte & Touche LLP, independent auditors, as stated in their report, which is incorporated herein by reference (which report expresses an unqualified opinion and includes an explanatory paragraph relating to the adoption of Statement of Financial Accounting Standards No. 143, “Accounting for Asset Retirement Obligations”), and have been so incorporated in reliance upon the report of such firm given upon their authority as experts in accounting and auditing.

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WHERE YOU CAN FIND MORE INFORMATION

        We file annual, quarterly and current reports, proxy statements and other information with the SEC. We have also filed registration statements on Form S-3, including exhibits, under the Securities Act of 1933 with respect to the common stock offered by this prospectus. This prospectus is a part of the registration statements, but does not contain all of the information included in the registration statements or the exhibits. You may read and copy the registration statements and any other document that we file at the SEC’s public reference rooms at 450 Fifth Street, N.W., Washington D.C. You can call the SEC at 1-800-SEC-0330 for further information on the operation of the public reference rooms. You can also find our public filings with the SEC on the internet at a web site maintained by the SEC located at http://www.sec.gov.

        We are “incorporating by reference” specified documents that we file with the SEC, which means:

        This prospectus incorporates by reference the documents listed below that we have previously filed with the SEC. They contain important information about us and our financial condition.

        We also incorporate by reference any future filings we make with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Securities Exchange Act of 1934 after the date of this prospectus and before the end of the offering of our common stock. These documents include periodic reports, such as Annual Reports on Form 10-K, Quarterly Reports on Form 10-Q, and Current Reports on Form 8-K, as well as proxy statements.

        You can obtain any of the documents incorporated by reference in this document from the SEC through the SEC’s web site at the address provided above. We will provide to you documents incorporated by reference without charge, upon your written or oral request, excluding any exhibits to those documents unless the exhibit is specifically incorporated by reference as an exhibit in this prospectus. You can obtain documents incorporated by reference in this prospectus by requesting them in writing or by telephone at the following:

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ALLIANT ENERGY CORPORATION

SHAREOWNER DIRECT PLAN

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PROSPECTUS

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                   , 20048

PART II

INFORMATION NOT REQUIRED IN PROSPECTUS

Item 14.        Other Expenses of Issuance and Distribution.

        All of the above fees and expenses will be paid by Alliant Energy Corporation (the “Registrant”) will pay all of the above fees and expenses.. Other than the Securities and Exchange Commission filing fee, all fees and expenses are estimated.

Item 15.        Indemnification of Directors and Officers.

        Pursuant to the provisions of the Wisconsin Business Corporation Law and Article VIII of the Registrant’s Bylaws, directors and officers of the Registrant are entitled to mandatory indemnification from the RegistrantsRegistrant against certain liabilities (which may include liabilities under the Securities Act of 1933) and expenses (i) to the extent such officers or directors are successful in the defense of a proceeding; and (ii) in proceedings in which the director or officer is not successful in defense thereof, unless it is determined that the director or officer breached or failed to perform his or her duties to the Registrant and such breach or failure constituted: (a) a willful failure to deal fairly with the Registrant or its shareowners in connection with a matter in which the director or officer had a material conflict of interest; (b) a violation of criminal law unless the director or officer had a reasonable cause to believe his or her conduct was lawful or had no reasonable cause to believe his or her conduct was unlawful; (c) a transaction from which the director or officer derived an improper personal profit; or (d) willful misconduct. Additionally, under the Wisconsin Business Corporation Law, directors of the Registrant are not subject to personal liability to the Registrant, its shareowners or any person asserting rights on behalf thereof, for certain breaches or failures to perform any duty resulting solely from their status as directors, except in circumstances paralleling those outlined in (a) through (d) above.

        The indemnification provided by the Wisconsin Business Corporation Law and the Registrant’s Bylaws is not exclusive of any other rights to which a director or officer of the Registrant may be entitled. The RegistrantsRegistrant also carries directors’ and officers’ liability insurance.

Item 16.        Exhibits and Financial Statement Schedules.

        The exhibits listed in the accompanying Exhibit Index are filed or incorporated by reference as part of this Registration Statement.

Item 17.        Undertakings.

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SIGNATURES

        Pursuant to the requirements of the Securities Act of 1933, the Registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-3 and has duly caused this Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Madison, State of Wisconsin, on March 31,April 9, 2004.

        Pursuant to the requirements of the Securities Act of 1933, this Registration Statement has been signed by the following persons in the capacities and on the dates indicated.

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EXHIBIT INDEX

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Documents incorporated by reference to filings made by Alliant Energy under the Securities Exchange Act of 1934, as amended (the “1934 Act”), are under File No. 1-9894. Documents incorporated by reference to filings made by WP&L under the 1934 Act are under File No. 0-337. Documents incorporated by reference to filings made by IP&L under the 1934 Act are under File No. 0-4117-1. Documents incorporated by reference to filings made by IPC under the 1934 Act are under File No. 1-3632.

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