Form 425

Filed by CBOT Holdings, Inc. Pursuant to

Rule 425 under the Securities Act of 1933 and

deemed filed pursuant to Rule 14a-12 under the

Securities Exchange Act of 1934

Subject Company

CBOT Holdings, Inc.

(Commission File No. 001-32650)

This morning, CME and CBOT announced that we have signed a definitive agreement to merge our two organizations to create the most extensive and diverse global derivatives exchange. The combined company, to be named CME Group Inc., a CME/Chicago Board of Trade Company, is expected to transform global derivatives markets, creating operational and cost efficiencies for customers and exchange members while delivering significant benefits to shareholders.

This merger will bring together two industry-leading innovators to create a single company, strengthening its ability to grow in an increasingly competitive market. We expect our customers to benefit from: the consolidation of trading floor operations into a single facility at CBOT; the eventual transition of CBOT products onto CME Globex®; distinct and innovative products and services; and the seamless continuation of current clearing services which secures existing margin benefits.

We expect the transaction to close by mid-year 2007, pending approvals by regulators, shareholders of both companies and CBOT members, as well as completion of customary closing conditions. Until the merger is completed, each company will continue to operate separately. All of the information that is publicly available is posted on www.cbot.com as well as www.cme.com.

We deeply value our relationship with you and look forward to continuing to provide the innovative products, technology and customer service expected from us.

Sincerely,

Bernie Dan

President and Chief Executive Officer

IMPORTANT MERGER INFORMATION

In connection with the proposed merger of CBOT Holdings, Inc. (“CBOT”) and the Chicago Mercantile Exchange Holdings Inc. (“CME”), the parties intend to file relevant materials with the Securities Exchange Commission (“SEC”), including a joint proxy statement/prospectus regarding the proposed transaction. Such documents, however, are not currently available. INVESTORS ARE URGED TO READ THE


JOINT PROXY STATEMENT/PROSPECTUS REGARDING THE PROPOSED TRANSACTION WHEN IT BECOMES AVAILABLE, BECAUSE IT WILL CONTAIN IMPORTANT INFORMATION. Investors will be able to obtain a free copy of the joint proxy statement/prospectus, as well as other filings containing information about CBOT and CME without charge, at the SEC’s website (http://www.sec.gov) once such documents are filed with the SEC. Copies of the joint proxy statement/prospectus can also be obtained, without charge, once they are filed with the SEC, by directing a request to CBOT Holdings, Inc., Attention: Investor Relations, at 141 West Jackson, Chicago, Illinois 60604 or calling (312) 435-3500.

CBOT, CME and their respective directors and executive officers and other members of management and employees may be deemed to be participants in the solicitation of proxies from CBOT shareholders in respect of the proposed transaction. Information regarding CBOT directors and executive officers is available in CBOT’s proxy statement for its 2006 annual meeting of stockholders, dated March 29, 2006. Additional information regarding the interests of such potential participants will be included in the joint proxy statement/prospectus and the other relevant documents filed with the SEC when they become available. This document shall not constitute an offer to sell or the solicitation of an offer to buy any securities, nor shall there be any sale of securities in any jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction. No offering of securities shall be made except by means of a prospectus meeting the requirements of Section 10 of the Securities Act of 1933, as amended.

FORWARD-LOOKING STATEMENTS

Certain statements in this document and its attachments may contain forward-looking information regarding CBOT, CME and the combined company after the completion of the transactions that are intended to be covered by the safe harbor for “forward-looking statements” provided by the Private Securities Litigation Reform Act of 1995. These statements include, but are not limited to, the benefits of the business combination transaction involving CBOT and CME including future financial and operating results, the new company’s plans, objectives, expectations and intentions and other statements that are not historical facts. Such statements are based upon the current beliefs and expectations of the management of CBOT and CME and are subject to significant risks and uncertainties. Actual results may differ from those set forth in the forward-looking statements.

The following factors, among others, could cause actual results to differ from those set forth in the forward-looking statements: the ability to obtain governmental approvals of the transaction on the proposed terms and schedule; the failure of CBOT shareholders or CME shareholders to approve the transaction; the risk that the businesses will not be integrated successfully; the risk that the cost savings and any other synergies from the transaction may not be fully realized or may take longer to realize than expected; disruption from the transaction making it more difficult to maintain relationships with customers, employees or suppliers; competition and its effect on pricing, spending, third-party relationships and revenues; social and political conditions such as war, political unrest or terrorism; general economic conditions and normal business uncertainty. Additional risks and factors are identified in CBOT’s filings with the SEC, including its Report on Form 10-K for the fiscal year ending December 31, 2005 which is available on CBOT’s website at http://www.cbot.com.

You should not place undue reliance on forward-looking statements, which speak only as of the date of this document. Except for any obligation to disclose material information under the Federal securities laws, CBOT undertakes no obligation to release publicly any revisions to any forward-looking statements to reflect events or circumstances after the date of this document.