Exhibit 1.1

$850,000,000

Washington Mutual, Inc.

Floating Rate Notes due January 15, 2010

4.20% Notes due January 15, 2010

UNDERWRITING AGREEMENT

December 13, 2004

LEHMAN BROTHERS INC.

MORGAN STANLEY & CO. INCORPORATED

As Representatives of the several Underwriters

c/o LEHMAN BROTHERS INC.

745 7^th Avenue

New York, New York 10019

Ladies and Gentlemen:

1. Introductory. Washington Mutual, Inc., a Washington corporation (the “Company”), proposes to issue and sell (i) $250,000,000 principal amount of its Floating Rate Notes due January 15, 2010 (the “Floating Rate Notes”) and (ii) $600,000,000 principal amount of its 4.20% Notes due January 15, 2010 (the “4.20% Notes” and together with the Floating Rate Notes, the “Offered Securities”) to be issued under an indenture, dated as of August 10, 1999 (as supplemented by a first supplemental indenture dated August 1, 2002 and a second supplemental indenture dated as of November 20, 2002, the “Indenture”), between the Company and The Bank of New York, as trustee (the “Trustee”). The Company hereby agrees with the several Underwriters named in Schedule A hereto (the “Underwriters”) as follows:

2. Representations and Warranties of the Company. The Company represents and warrants to, and agrees with, the several Underwriters that:

(a) Registration statement (No. 333-109921) and registration statement (No. 333-102991), including a combined prospectus relating to the Offered Securities, have been filed with the Securities and Exchange Commission (the “Commission”) and have become effective. Such registration statements, as amended at the time of this Agreement, are hereinafter referred to as the “Registration Statements”, and the combined prospectus included therein, as supplemented to reflect the terms of the Offered Securities and the terms of offering thereof, as first filed with the Commission pursuant to

and in accordance with Rule 424(b) (“Rule 424(b)”) under the Securities Act of 1933 (the “Act”), including all material incorporated by reference therein, is hereinafter referred to as the “Prospectus”. No document has been or will be prepared or distributed in reliance on Rule 434 under the Act.

(b) On its respective effective date, each of the Registration Statements conformed in all material respects to the requirements of the Act, the Trust Indenture Act of 1939 (the “Trust Indenture Act”) and the rules and regulations of the Commission (the “Rules and Regulations”) and did not include any untrue statement of a material fact or omit to state any material fact required to be stated therein or necessary to make the statements therein not misleading, and on the date of this Agreement, the Registration Statements and the Prospectus conformed in all respects to the requirements of the Act, the Trust Indenture Act and the Rules and Regulations, and neither document will include any untrue statement of a material fact or omit to state any material fact required to be stated therein or necessary to make the statements therein not misleading, except that the foregoing does not apply to statements in or omissions from any of such documents based upon written information furnished to the Company by any Underwriter through the Representatives, if any, specifically for use therein.

(c) The Company has been duly incorporated and is an existing corporation under the laws of the State of Washington, with corporate power and authority to own its properties and conduct its business as described in the Prospectus; and the Company is duly qualified to do business as a foreign corporation in good standing in all other jurisdictions in which its ownership or lease of property or the conduct of its business requires such qualification.

(d) Each of Washington Mutual Bank, FA, Washington Mutual Bank and New American Capital, Inc. (each, a “Significant Subsidiary” and collectively, the “Significant Subsidiaries”) has been duly incorporated and is a validly existing corporation or depository institution in good standing under the laws of the jurisdiction of its incorporation, with power and authority (corporate and other) to own its properties and conduct its business as described in the Prospectus; and each Significant Subsidiary is duly qualified to do business as a foreign corporation in good standing in all other jurisdictions in which its ownership or lease of property or the conduct of its business requires such qualification, except for such failure to qualify which would not, individually or in the aggregate, have a material adverse effect on the condition (financial or other), business, properties or results of operations of the Company and its subsidiaries taken as a whole (a “Material Adverse Effect”); the Company has an authorized capitalization as set forth in the Prospectus; all of the issued and outstanding capital stock of each Significant Subsidiary has been duly authorized and validly issued and is fully paid and nonassessable; and the capital stock of each Significant Subsidiary is owned by the Company, directly or through subsidiaries, free from liens, encumbrances and defects.

(e) The Company has been duly registered as a savings and loan holding company under the applicable provisions of the Home Owners’ Loan Act; the Company and each of its subsidiaries are in compliance in all material respects with all laws administered by and regulations of the Federal Deposit Insurance Corporation (“FDIC”), the Office of Thrift Supervision and any other federal or state bank regulatory authority (the “Bank Regulatory Authorities”) with jurisdiction over the Company or any of its subsidiaries, other than where such failures to comply would not, individually or in the aggregate, have a Material Adverse Effect; and neither the Company nor any of its subsidiaries is a party to any written agreement or memorandum of understanding with, or a party to any commitment letter or similar undertaking to, or is subject to any order or directive by, or is a

recipient of any extraordinary supervisory letter from, or has adopted any board resolutions at the request of, any Bank Regulatory Authority which restricts materially the conduct of its business, or in any manner relates to its capital adequacy, its credit policies or its management, nor have any of them been advised by any Bank Regulatory Authority that it is contemplating issuing or requesting (or is considering the appropriateness of issuing or requesting) any such order, decree, agreement, memorandum of understanding, extraordinary supervisory letter, commitment letter or similar submission, or any such board resolutions.

(f) The Indenture has been duly authorized, executed and delivered by the Company and has been duly qualified under the Trust Indenture Act with respect to the Offered Securities registered thereby; the Offered Securities have been duly authorized; and when the Offered Securities are delivered and paid for pursuant to this Agreement on the Closing Date (as defined below), such Offered Securities will have been duly executed, authenticated, issued and delivered and will conform to the description thereof contained in the Prospectus and the Indenture and such Offered Securities will constitute valid and legally binding obligations of the Company, enforceable in accordance with their terms, subject to bankruptcy, insolvency, fraudulent transfer, reorganization, moratorium and similar laws of general applicability relating to or affecting creditors’ rights and to general equity principles.

(g) No consent, approval, authorization, or order of, or filing with, any governmental agency or body or any court is required for the consummation of the transactions contemplated by this Agreement in connection with the issuance and sale of the Offered Securities by the Company, except such as have been obtained and made under the Act and the Trust Indenture Act and such as may be required under state securities laws.

(h) The execution, delivery and performance of the Indenture and this Agreement, and the issuance and sale of the Offered Securities and compliance with the terms and provisions thereof will not result in a breach or violation of any of the terms and provisions of, or constitute a default under, (i) any statute, any rule, regulation or order of any governmental agency or body or any court, domestic or foreign, having jurisdiction over the Company or any Significant Subsidiary or any of their properties, (ii) any agreement or instrument to which the Company or any Significant Subsidiary is a party or by which the Company or any Significant Subsidiary is bound or to which any of the properties of the Company or any Significant Subsidiary is subject, except for such breach, violation or default which would not individually or in the aggregate have a Material Adverse Effect, or (iii) the charter or by-laws of the Company or any Significant Subsidiary; and the Company has full power and authority to authorize, issue and sell the Offered Securities as contemplated by this Agreement.

(i) This Agreement has been duly authorized, executed and delivered by the Company.

(j) Except as disclosed in the Prospectus and except for such failure that would not individually or in the aggregate have a Material Adverse Effect, the Company and its subsidiaries have good and marketable title to all real properties and all other properties and assets owned by them, in each case free from liens, encumbrances and defects that would affect the value thereof or interfere with the use made or to be made thereof by them; and except as disclosed in the Prospectus and except for such failure that would not individually or in the aggregate have a Material Adverse Effect, the Company and its subsidiaries hold all leased real or personal property

under valid and enforceable leases with no exceptions that would interfere with the use made or to be made thereof by them.

(k) The conditions for use of Form S-3, as set forth in the General Instructions thereto, have been satisfied.

(l) The Company and its subsidiaries possess adequate certificates, authorities or permits issued by appropriate governmental agencies or bodies necessary to conduct the business now operated by them, except where the failure to so possess would not individually or in the aggregate have a Material Adverse Effect, and have not received any notice of proceedings relating to the revocation or modification of any such certificate, authority or permit that, if determined adversely to the Company or any of its subsidiaries, would individually or in the aggregate have a Material Adverse Effect.

(m) No labor dispute with the employees of the Company or any Significant Subsidiary exists or, to the knowledge of the Company, is imminent that might individually or in the aggregate have a Material Adverse Effect.

(n) The Company and its subsidiaries own, possess or can acquire on reasonable terms, adequate trademarks, trade names and other rights to inventions, know-how, patents, copyrights, confidential information and other intellectual property (collectively, “intellectual property rights”) necessary to conduct the business now operated by them, or presently employed by them, and have not received any notice of infringement of or conflict with asserted rights of others with respect to any intellectual property rights that, if determined adversely to the Company or any of the Significant Subsidiaries, would individually or in the aggregate have a Material Adverse Effect.

(o) Except as disclosed in the Prospectus, there are no pending actions, suits or proceedings against or affecting the Company, any of its subsidiaries or any of their respective properties that, if determined adversely to the Company or any of its subsidiaries, would individually or in the aggregate have a Material Adverse Effect, or would materially and adversely affect the ability of the Company to perform its obligations under the Indenture or this Agreement, or which are otherwise material in the context of the sale of the Offered Securities; and no such actions, suits or proceedings are threatened or, to the Company’s knowledge, contemplated.

(p) The financial statements (including the related notes and supporting schedules) included or incorporated by reference in the Registration Statements and the Prospectus present fairly the financial position of the Company and its consolidated subsidiaries as of the dates shown and their results of operations and cash flows for the periods shown, and, except as otherwise disclosed in the Prospectus, such financial statements have been prepared in conformity with the generally accepted accounting principles in the United States applied on a consistent basis.

(q) Except as disclosed in the Prospectus, since the date of the latest financial statements included or incorporated by reference in the Prospectus there has been no material adverse change, nor any development or event involving a prospective material adverse change, in the condition (financial or other), business, properties or results of operations of the Company and its subsidiaries taken as a whole, and, except as disclosed in or contemplated by the Prospectus, there

has been no dividend or distribution of any kind declared, paid or made by the Company on any class of its capital stock.

(r) The Company is not and, after giving effect to the offering and sale of the Offered Securities and the application of the proceeds thereof as described in the Prospectus, will not be an “investment company” as defined in the Investment Company Act of 1940.

(s) The Company and each of its subsidiaries have insurance covering their respective properties, operations, personnel and businesses, which insurance is in amounts and insures against such losses and risks as are prudent and customary in the business in which the Company and its subsidiaries are engaged. Neither the Company nor any of its subsidiaries has received notice from any insurer or agent of such insurer that capital improvements or other expenditures are required or necessary to be made in order to continue such insurance.

(t) None of the proceeds of the sale of the Securities will be used, directly or indirectly, for the purpose of purchasing or carrying any margin security, for the purpose of reducing or retiring any indebtedness which was originally incurred to purchase or carry any margin security or for any other purpose which might cause any of the Securities to be considered a “purpose credit” within the meanings of Regulation U of the Federal Reserve Board.

(u) The Company maintains (i) effective internal control over financial reporting as defined in Rule 13a-15 under the Securities Exchange Act of 1934, as amended, and (ii) a system of internal accounting controls sufficient to provide reasonable assurance that (A) transactions are executed in accordance with management’s general or specific authorizations; (B) transactions are recorded as necessary to permit preparation of financial statements in conformity with generally accepted accounting principles and to maintain asset accountability; (C) access to assets is permitted only in accordance with management’s general or specific authorization; and (D) the recorded accountability for assets is compared with the existing assets at reasonable intervals and appropriate action is taken with respect to any differences.

(v) Based on its evaluation of its internal controls over financial reporting, the Company is not aware of (i) any significant deficiency or material weakness in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect the Company’s ability to record, process, summarize and report financial information; or (ii) any fraud, whether or not material, that involves management or other employees who have a significant role in the Company’s internal control over financial reporting.

3. Purchase, Sale and Delivery of Offered Securities. On the basis of the representations, warranties and agreements herein contained, but subject to the terms and conditions herein set forth, the Company agrees to sell to the Underwriters, and the Underwriters agree, severally and not jointly, to purchase from the Company, (i) at a purchase price of 99.675% of the principal amount thereof plus accrued interest from December 20, 2004 to the Closing Date (as hereinafter defined), the respective principal amounts of Floating Rate Notes set forth opposite the names of the Underwriters in Schedule A hereto and (ii) at a purchase price of 99.522% of the principal amount thereof plus accrued interest from December 20, 2004 to the Closing Date (as hereinafter defined), the respective principal amounts of the 4.20% Notes set forth opposite the names of the Underwriters in Schedule A hereto.

The Company will deliver against payment of the purchase price of the Offered Securities in the form of one or more permanent global Securities (the “Global Securities”) deposited with the Trustee as custodian for The Depository Trust Company (the “DTC”) and registered in the name of Cede & Co., as nominee for DTC. Interests in any permanent Global Securities will be held only in book-entry form through DTC, except in the limited circumstances described in the Prospectus. Payment for the Offered Securities shall be made by the Underwriters in federal (same day) funds, by official bank check or checks or wire transfer to an account at a bank acceptable to the Representatives drawn to the order of Washington Mutual, Inc. at their office at 10 A.M., (New York time), on December 20, 2004, or at such other time not later than seven full business days thereafter as the Representatives and the Company determine, such time being herein referred to as the “Closing Date”, against delivery to the Trustee as custodian for DTC of the Global Securities representing all of the Offered Securities. The Global Securities will be made available for checking at the office of Cleary, Gottlieb, Steen & Hamilton, One Liberty Plaza, New York, New York 10006, at least 24 hours prior to the Closing Date.

4. Offering by Underwriters. It is understood that the several Underwriters propose to offer the Offered Securities for sale to the public as set forth in the Prospectus. In connection with the offering, the Underwriters shall reimburse the Company $212,500 of the Company’s expenses related to the offering.

5. Certain Agreements of the Company. The Company agrees with the several Underwriters that it will furnish to counsel for the Underwriters one signed copy of each of the Registration Statements, including all exhibits, in the form it became effective and of all amendments thereto and that, in connection with each offering of Offered Securities:

(a) The Company will file the Prospectus with the Commission pursuant to and in accordance with Rule 424(b) not later than the second business day following the execution and delivery of this Agreement.

(b) The Company will advise the Representatives promptly of any proposal to amend or supplement either of the Registration Statements or the Prospectus and will afford the Representatives a reasonable opportunity to comment on any such proposed amendment or supplement; and the Company will also advise the Representatives promptly of the filing of any such amendment or supplement and of the institution by the Commission of any stop order proceedings in respect of either of the Registration Statements or of any part thereof and will use its best efforts to prevent the issuance of any such stop order and to obtain as soon as possible its lifting, if issued.

(c) If, at any time when a prospectus relating to the Offered Securities is required to be delivered under the Act in connection with sales by any Underwriter or dealer, any event occurs as a result of which the Prospectus as then amended or supplemented would include an untrue statement of a material fact or omit to state any material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading, or if it is necessary at any time to amend the Prospectus to comply with the Act, the Company promptly will notify the Representatives of such event and will promptly prepare and file with the Commission, at its own expense, an amendment or supplement which will correct such statement or omission or an amendment which will effect such compliance. Neither the Representatives’ consent to, nor the Underwriters’ delivery of,

any such amendment or supplement shall constitute a waiver of any of the conditions set forth in Section 5 hereof.

(d) As soon as practicable, but not later than 16 months after the date of this Agreement, the Company will make generally available to its security holders an earnings statement covering a period of at least 12 months beginning after the later of (i) the effective date of the Registration Statements relating to the Offered Securities, (ii) the effective date of the most recent post-effective amendment to the Registration Statements to become effective prior to the date of this Agreement and (iii) the date of the Company’s most recent Annual Report on Form 10-K filed with the Commission prior to the date of this Agreement, which will satisfy the provisions of Section 11(a) of the Act.

(e) The Company will furnish to the Representatives copies of the Registration Statements, including all exhibits, any related preliminary prospectus, any related preliminary prospectus supplement, the Prospectus and all amendments and supplements to such documents, in each case as soon as available and in such quantities as the Representatives may reasonably request. The Company will pay the expenses of printing and distributing to the Underwriters all such documents.

(f) The Company will arrange for the qualification of the Offered Securities for sale and the determination of their eligibility for investment under the laws of such jurisdictions as the Representatives shall designate and will continue such qualifications in effect so long as required for the distribution, provided that the Company and its subsidiaries shall not be obligated to qualify as foreign corporations in any jurisdiction in which they are not so qualified or to file a general consent to service of process in any jurisdiction.

(g) During the period of five years hereafter, the Company will furnish to the Representatives and, upon request, to each of the other Underwriters, as soon as practicable after the end of each fiscal year, a copy of its annual report to stockholders for such year; and the Company will furnish to the Representatives as soon as available, a copy of each report and any definitive proxy statement of the Company filed with the Commission under the Securities Exchange Act of 1934, as amended (the “Exchange Act”) or mailed to stockholders.

(h) The Company will pay all expenses incident to the performance of its obligations under this Agreement, for any filing fees and other expenses (including fees and disbursements of counsel) incurred in connection with qualification of the Offered Securities for sale under the laws of such jurisdictions as the Representatives may designate and the printing of memoranda relating thereto, for any fees charged by investment rating agencies for the rating of the Offered Securities, for any travel expenses of the Company’s officers and employees and any other expenses of the Company in connection with attending or hosting meetings with prospective purchasers of the Offered Securities and for expenses incurred in distributing the Prospectus, any preliminary prospectus, any preliminary prospectus supplement or any other amendments or supplements to the Prospectus to the Underwriters.

(i) The Company will not offer, sell, contract to sell, pledge or otherwise dispose of, directly or indirectly, or file with the Commission a registration statement under the Act relating to debt securities issued or guaranteed by the Company and having a maturity of more than one year from the date of issue, or publicly disclose the intention to make any such offer, sale, pledge, disposition or filing, without the prior written consent of the Representatives for a period beginning at the date

of this Agreement and ending at the later of the Closing Date or the lifting of trading restrictions by the Representatives.

6. Conditions of the Obligations of the Underwriters. The obligations of the several Underwriters to purchase and pay for the Offered Securities will be subject to the accuracy of the representations and warranties on the part of the Company herein, to the accuracy of the statements of Company officers made pursuant to the provisions hereof, to the performance by the Company of its obligations hereunder and to the following additional conditions precedent:

(a) On or prior to the Closing Date, the Representatives shall have received a letter, dated the date of delivery thereof, of Deloitte & Touche LLP confirming that they are independent public accountants within the meaning of the Act and the applicable published Rules and Regulations thereunder and stating to the effect that:

(i) in their opinion the consolidated financial statements examined by them and included in the Prospectus comply as to form in all material respects with the applicable accounting requirements of the Exchange Act and the related published Rules and Regulations;

(ii) they have performed the procedures specified by the American Institute of Certified Public Accountants for a review of interim financial information as described in Statement of Auditing Standards No. 100, Interim Financial Information, as amended, on any unaudited interim consolidated financial statements included in the Registration Statements;

(iii) on the basis of the review referred to in clause (ii) above, a reading of the latest available unaudited interim consolidated financial statements of the Company, inquiries of officials of the Company who have responsibility for financial and accounting matters and other specified procedures, nothing came to their attention that caused them to believe that:

(A) the unaudited interim consolidated financial statements, if any, and any summary financial statements included in the Prospectus do not comply as to form in all material respects with the applicable accounting requirements of the Act and the related published Rules and Regulations or any material modifications should be made to such unaudited interim consolidated financial statements and summary financial statements for them to be in conformity with generally accepted accounting principles in the United States;

(B) if any unaudited “capsule” information is contained in the Prospectus, the unaudited consolidated net sales, net operating income, net income and net income per share amounts or other amounts constituting such “capsule” information and described in such letter do not agree with the corresponding amounts set forth in the unaudited consolidated financial statements or were not determined on a basis substantially consistent with that of the corresponding amounts in the audited statements of income;

(C) at the date of the latest available balance sheet read by such accountants, or at a subsequent specified date not more than three business days prior to the date of the such letter, there was any change in the number of common shares outstanding or any increase in other borrowings of the Company and its consolidated subsidiaries or, at the date of the latest available balance sheet read by such accountants, there was any decrease in stockholders’ equity or the combined balance of cash and cash equivalents, federal funds sold and securities purchased under resale agreements, and available-for-sale securities of the Company, as compared with amounts shown on the latest balance sheet included in the Prospectus; or

(D) for the period from the closing date of the latest income statement included in the Prospectus to the closing date of the latest available income statement read by such accountants there were any decreases, as compared with the corresponding period of the previous year and with the period of corresponding length ended the date of the latest income statement included in the Prospectus, in consolidated net interest income, net income, the combined balance of net income before taxes and total interest expense, net income per share, or diluted net income per share;

except in all cases set forth in clauses (C) and (D) above for changes, increases or decreases which the Prospectus discloses have occurred or may occur or which are described in such letter; and

(iv) they have compared specified dollar amounts (or percentages derived from such dollar amounts) and other financial information contained in the Prospectus (in each case to the extent that such dollar amounts, percentages and other financial information are derived from the general accounting records of the Company and its subsidiaries subject to the internal controls of the Company’s accounting system or are derived directly from such records by analysis or computation) with the results obtained from inquiries, a reading of such general accounting records and other procedures specified in such letter and have found such dollar amounts, percentages and other financial information to be in agreement with such results, except as otherwise specified in such letter.

All financial statements and schedules included in material incorporated by reference into the Prospectus shall be deemed included in the Prospectus for purposes of this subsection.

(b) The Prospectus shall have been filed with the Commission in accordance with the Rules and Regulations and Section 5(a) of this Agreement. No stop order suspending the effectiveness of either of the Registration Statements or of any part thereof shall have been issued and no proceedings for that purpose shall have been instituted or, to the knowledge of the Company or any Underwriter, shall be contemplated by the Commission.

(c) Subsequent to the execution and delivery of this Agreement, there shall not have occurred (i) any change, or any development or event involving a prospective change, in the condition (financial or other), business, properties or results of operations of the Company and its subsidiaries taken as one enterprise which, in the judgment of the Representatives, is material and

adverse and makes it impractical or inadvisable to proceed with completion of the public offering or the sale of and payment for the Offered Securities; (ii) any downgrading in the rating of any debt securities of the Company by any “nationally recognized statistical rating organization” (as defined for purposes of Rule 436(g) under the Act), or any public announcement that any such organization has under surveillance or review its rating of any debt securities of the Company (other than an announcement with positive implications of a possible upgrading, and no implication of a possible downgrading, of such rating); (iii) any change in U.S. or international financial, political or economic conditions or currency exchange rates or exchange controls as would, in the judgment of the Representatives, be likely to prejudice materially the success of the proposed issue, sale or distribution of the Offered Securities, whether in the primary market or in respect of dealings in the secondary market; (iv) any material suspension or material limitation of trading in securities generally on the New York Stock Exchange, or any setting of minimum prices for trading on such exchange, or any suspension of trading of any securities of the Company on any exchange or in the over-the-counter market; (v) any banking moratorium declared by U.S. federal or New York authorities; (vi) any major disruption of settlements of securities or clearance services in the United States or (vii) any attack on, outbreak or escalation of hostilities or act of terrorism involving the United States, any declaration of war by Congress or any other national or international calamity or emergency if, in the judgment of the Representatives, the effect of any such attack, outbreak, escalation, act, declaration, calamity or emergency makes it impractical or inadvisable to proceed with completion of the public offering or the sale of and payment for the Offered Securities.

(d) The Representatives shall have received an opinion, dated the Closing Date, of Heller Ehrman White & McAuliffe LLP, counsel for the Company, in the form satisfactory to the Representatives, to the effect that:

(i) The Company has been duly incorporated and is an existing corporation under the laws of the State of Washington, with corporate power and authority to own its properties and conduct its business as described in the Prospectus;

(ii) The Significant Subsidiaries have been duly incorporated and are existing corporations or depository institutions in good standing under the laws of their respective jurisdiction, with corporate power and authority to own their properties and conduct their business as described in the Prospectus;

(iii) The Indenture has been duly authorized, executed and delivered by the Company and has been duly qualified under the Trust Indenture Act; the Offered Securities have been duly authorized and issued by the Company, and assuming due authentication thereof by the trustee under the Indenture and upon payment and delivery in accordance with this Agreement, will be duly and validly issued and outstanding; the Indenture and the Offered Securities constitute valid and binding obligations of the Company enforceable in accordance with their terms, subject to bankruptcy, insolvency, fraudulent transfer, reorganization, moratorium and similar laws of general applicability relating to or affecting creditors’ rights and to general equity principles whether such enforceability is considered in a proceeding in equity or at law; and the Offered Securities conform to the description thereof contained in the Prospectus;

(iv) No consent, approval, authorization or order of, or filing with, any governmental agency or body or any court is required for the consummation of the transactions contemplated by this Agreement (including the provisions of this Agreement) in connection with the issuance or sale of the Offered Securities by the Company, except such as have been obtained and made under the Act and the Trust Indenture Act and such as may be required under state securities laws;

(v) The execution, delivery and performance of the Indenture or this Agreement, and the issuance and sale of the Offered Securities and compliance with the terms and provisions thereof will not result in a breach or violation of any of the terms and provisions of, or constitute a default under, (i) any statute, any rule or regulation of any governmental agency or body or, to such counsel’s knowledge, any order or judgment of any court having jurisdiction over the Company or any subsidiary of the Company or any of their properties, (ii) pursuant to any agreement listed as an exhibit to the Company’s reports filed by the company pursuant to the Exchange Act, or (iii) the charter or by-laws of the Company or any Significant Subsidiary, and the Company has full corporate power and authority to authorize, issue and sell the Offered Securities as contemplated by this Agreement;

(vi) The Registration Statements have become effective under the Act, the Prospectus was filed with the Commission pursuant to the subparagraph of Rule 424(b) specified in such opinion on the date specified therein, and, to the best of the knowledge of such counsel, no stop order suspending the effectiveness of either of the Registration Statements or any part thereof has been issued and no proceedings for that purpose have been instituted or are pending or contemplated under the Act, and the Registration Statements relating to the Offered Securities, as of their effective dates, the Registration Statements and the Prospectus, as of the date of this Agreement, and any amendment or supplement thereto, as of its date, complied as to form in all material respects with the requirements of the Act, the Trust Indenture Act and the Rules and Regulations; such counsel have no reason to believe that either of the Registration Statements, as of their effective date, as of the date of this Agreement or as of the Closing Date, or any amendment thereto, as of its date or as of the Closing Date, contained any untrue statement of a material fact or omitted to state any material fact required to be stated therein or necessary to make the statements therein not misleading or that the Prospectus, as of the date of this Agreement or as of the Closing Date, or any amendment or supplement thereto, as of its date or as of the Closing Date, contained any untrue statement of a material fact or omitted to state any material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading; the descriptions in the Registration Statements and Prospectus of statutes, legal and governmental proceedings and contracts and other documents are accurate and fairly present the information required to be shown; and such counsel do not know of any legal or governmental proceedings required to be described in the Prospectus which are not described as required or of any contracts or documents of a character required to be described in the Registration Statements or Prospectus or to be filed as exhibits to the Registration Statements which are not described and filed as required; it being understood that such counsel need

express no opinion as to the financial statements or other financial data contained in the Registration Statements or the Prospectus;

(vii) This Agreement has been duly authorized, executed and delivered by the Company; and

(viii) The Company is duly registered as a savings and loan holding company under the applicable provisions of the Home Owners’ Loan Act. To such counsel’s knowledge, neither the Company nor any of its subsidiaries is a party to any written agreement or memorandum of understanding with, or a party to any commitment letter or similar undertaking to, or is subject to any order or directive by, or is a recipient of any extraordinary supervisory letter from, or has adopted any board resolutions at the request of, any Bank Regulatory Authority which restricts materially the conduct of its business, or in any manner relates to its capital adequacy, its credit policies or its management, nor have any of them been advised by any Bank Regulatory Authority that it is contemplating issuing or requesting (or is considering the appropriateness of issuing or requesting) any such order, decree, agreement, memorandum of understanding, extraordinary supervisory letter, commitment letter or similar submission, or any such board resolutions.

(e) The Representatives shall have received from Cleary, Gottlieb, Steen & Hamilton, counsel for the Underwriters, such opinion or opinions, dated such Closing Date, with respect to the validity of the Offered Securities delivered on such Closing Date, the Registration Statements, the Prospectus and other related matters as the Representatives may require, and the Company shall have furnished to such counsel such documents as they request for the purpose of enabling them to pass upon such matters. In rendering such opinion, Cleary, Gottlieb, Steen & Hamilton may rely as to matters governed by Washington law upon the opinion of Heller Ehrman White & McAuliffe LLP referred to above.

(f) The Representatives shall have received a certificate, dated the Closing Date, of the President or any Vice President and a principal financial or accounting officer of the Company in which such officers, to the best of their knowledge after reasonable investigation, shall state that the representations and warranties of the Company in this Agreement are true and correct, that the Company has complied with all agreements and satisfied all conditions on its part to be performed or satisfied hereunder at or prior to the Closing Date, that no stop order suspending the effectiveness of the Registration Statements or of any part thereof has been issued and no proceedings for that purpose have been instituted or are contemplated by the Commission and that, subsequent to the date of the most recent financial statements included or incorporated by reference in the Prospectus, there has been no material adverse change, nor any development or event involving a prospective material adverse change, in the condition (financial or other), business, properties or results of operations of the Company and its subsidiaries taken as a whole except as set forth in or contemplated by the Prospectus or as described in such certificate.

The Company will furnish the Representatives with such conformed copies of such opinions, certificates, letters and documents as the Representatives reasonably request. The Representatives may in their sole

discretion waive on behalf of the Underwriters compliance with any conditions to the obligations of the Underwriters hereunder, whether in respect of the Closing Date or otherwise.

7. Indemnification and Contribution.

(a) The Company will indemnify and hold harmless each Underwriter, its partners, directors and officers and each person, if any, who controls such Underwriter within the meaning of Section 15 of the Act, against any losses, claims, damages or liabilities, joint or several, to which such Underwriter may become subject, under the Act or otherwise, insofar as such losses, claims, damages or liabilities (or actions in respect thereof) arise out of or are based upon any untrue statement or alleged untrue statement of any material fact contained in either of the Registration Statements, the Prospectus, or any amendment or supplement thereto, or any related preliminary prospectus or preliminary prospectus supplement, or arise out of or are based upon the omission or alleged omission to state therein a material fact required to be stated therein or necessary to make the statements therein not misleading, and will reimburse each Underwriter for any legal or other expenses reasonably incurred by such Underwriter in connection with investigating or defending any such loss, claim, damage, liability or action as such expenses are incurred; provided, however, (i) that the Company will not be liable in any such case to the extent that any such loss, claim, damage or liability arises out of or is based upon an untrue statement or alleged untrue statement in or omission or alleged omission from any of such documents in reliance upon and in conformity with written information furnished to the Company by any Underwriter through the Representatives specifically for use therein, it being understood and agreed that the only such information furnished by any Underwriter consists of the information described as such in subsection (b) below; and provided, further, that with respect to any untrue statement or alleged untrue statement in or omission or alleged omission from any preliminary prospectus the indemnity agreement contained in this subsection (a) shall not inure to the benefit of any Underwriter from whom the person asserting any such losses, claims, damages or liabilities purchased the Offered Securities concerned, to the extent that a prospectus relating to such Offered Securities was required to be delivered by such Underwriter under the Act in connection with such purchase and any such loss, claim, damage or liability of such Underwriter results from the fact that there was not sent or given to such person, at or prior to the written confirmation of the sale of such Offered Securities to such person, a copy of the Prospectus (exclusive of material incorporated by reference) if the Company had previously furnished copies thereof to such Underwriter.

(b) Each Underwriter will severally and not jointly indemnify and hold harmless the Company, its directors and officers and each person, if any, who controls the Company within the meaning of Section 15 of the Act, against any losses, claims, damages or liabilities to which the Company may become subject, under the Act or otherwise, insofar as such losses, claims, damages or liabilities (or actions in respect thereof) arise out of or are based upon any untrue statement or alleged untrue statement of any material fact contained in either of the Registration Statements, the Prospectus, or any amendment or supplement thereto, or any related preliminary prospectus or preliminary prospectus supplement, or arise out of or are based upon the omission or the alleged omission to state therein a material fact required to be stated therein or necessary to make the statements therein not misleading, in each case to the extent, but only to the extent, that such untrue statement or alleged untrue statement or omission or alleged omission was made in reliance upon and in conformity with written information furnished to the Company by such Underwriter through the Representatives specifically for use therein, and will reimburse any legal or other expenses reasonably incurred by the Company in connection with investigating or defending any such loss, claim, damage, liability or action as such expenses are incurred, it being understood and agreed that the only such

information furnished by any Underwriter consists of the following information in the Prospectus furnished on behalf of each Underwriter: the concession figures appearing in the second paragraph under the caption “Underwriting” and the information contained in the fourth paragraph under the caption “Underwriting.”

(c) Promptly after receipt by an indemnified party under this Section of notice of the commencement of any action, such indemnified party will, if a claim in respect thereof is to be made against the indemnifying party under subsection (a) or (b) above, notify the indemnifying party of the commencement thereof; but the omission so to notify the indemnifying party will not relieve it from any liability which it may have to any indemnified party otherwise than under subsection (a) or (b) above. In case any such action is brought against any indemnified party and it notifies the indemnifying party of the commencement thereof, the indemnifying party will be entitled to participate therein and, to the extent that it may wish, jointly with any other indemnifying party similarly notified, to assume the defense thereof, with counsel satisfactory to such indemnified party (who shall not, except with the consent of the indemnified party, be counsel to the indemnifying party), and after notice from the indemnifying party to such indemnified party of its election so to assume the defense thereof, the indemnifying party will not be liable to such indemnified party under this Section for any legal or other expenses subsequently incurred by such indemnified party in connection with the defense thereof other than reasonable costs of investigation. No indemnifying party shall, without the prior written consent of the indemnified party, effect any settlement of any pending or threatened action in respect of which any indemnified party is or could have been a party and indemnity could have been sought hereunder by such indemnified party unless such settlement (i) includes an unconditional release of such indemnified party from all liability on any claims that are the subject matter of such action and (ii) does not include a statement as to, or an admission of, fault, culpability or a failure to act by or on behalf of an indemnified party.

(d) If the indemnification provided for in this Section is unavailable or insufficient to hold harmless an indemnified party under subsection (a) or (b) above, then each indemnifying party shall contribute to the amount paid or payable by such indemnified party as a result of the losses, claims, damages or liabilities referred to in subsection (a) or (b) above (i) in such proportion as is appropriate to reflect the relative benefits received by the Company on the one hand and the Underwriters on the other from the offering of the Securities or (ii) if the allocation provided by clause (i) above is not permitted by applicable law, in such proportion as is appropriate to reflect not only the relative benefits referred to in clause (i) above but also the relative fault of the Company on the one hand and the Underwriters on the other in connection with the statements or omissions which resulted in such losses, claims, damages or liabilities as well as any other relevant equitable considerations. The relative benefits received by the Company on the one hand and the Underwriters on the other shall be deemed to be in the same proportion as the total net proceeds from the offering (before deducting expenses) received by the Company bear to the total underwriting discounts and commissions received by the Underwriters. The relative fault shall be determined by reference to, among other things, whether the untrue or alleged untrue statement of a material fact or the omission or alleged omission to state a material fact relates to information supplied by the Company or the Underwriters and the parties’ relative intent, knowledge, access to information and opportunity to correct or prevent such untrue statement or omission. The amount paid by an indemnified party as a result of the losses, claims, damages or liabilities referred to in the first sentence of this subsection (d) shall be deemed to include any legal or other expenses reasonably incurred by such indemnified party in connection with investigating or defending any action or claim which is the subject of this subsection (d). Notwithstanding the provisions of this subsection (d), no Underwriter shall be required to contribute any amount in excess of the amount by which the total price at which the Securities underwritten by it and distributed to the public were offered to the public exceeds the amount of any

damages which such Underwriter has otherwise been required to pay by reason of such untrue or alleged untrue statement or omission or alleged omission. No person guilty of fraudulent misrepresentation (within the meaning of Section 11(f) of the Act) shall be entitled to contribution from any person who was not guilty of such fraudulent misrepresentation. The Underwriters’ obligations in this subsection (d) to contribute are several in proportion to their respective underwriting obligations and not joint.

(e) The obligations of the Company under this Section shall be in addition to any liability which the Company may otherwise have and shall extend, upon the same terms and conditions, to each person, if any, who controls any Underwriter within the meaning of the Act; and the obligations of the Underwriters under this Section shall be in addition to any liability which the respective Underwriters may otherwise have and shall extend, upon the same terms and conditions, to each director of the Company, to each officer of the Company who has signed either of the Registration Statements and to each person, if any, who controls the Company within the meaning of the Act.

8. Default of Underwriters. If any Underwriter or Underwriters default in their obligations to purchase the Offered Securities hereunder on the Closing Date and the aggregate principal amount of the Offered Securities that such defaulting Underwriter or Underwriters agreed but failed to purchase does not exceed 10% of the total principal amount of the Offered Securities that the Underwriters are obligated to purchase on such Closing Date, the Representatives may make arrangements satisfactory to the Company for the purchase of such Offered Securities by other persons, including any of the Underwriters, but if no such arrangements are made by such Closing Date, the non-defaulting Underwriters shall be obligated severally, in proportion to their respective commitments hereunder, to purchase the Offered Securities that such defaulting Underwriters agreed but failed to purchase on such Closing Date. If any Underwriter or Underwriters so default and the aggregate principal amount of the Offered Securities with respect to which such default or defaults occur exceeds 10% of the total principal amount of the Offered Securities that the Underwriters are obligated to purchase on such Closing Date and arrangements satisfactory to the Representatives and the Company for the purchase of such Offered Securities by other persons are not made within 36 hours after such default, this Agreement will terminate without liability on the part of any non-defaulting Underwriter, or the Company, except as provided in Section 9. As used in this Agreement, the term “Underwriter” includes any person substituted for an Underwriter under this Section. Nothing herein will relieve a defaulting Underwriter from liability for its default.

9. Survival of Certain Representations and Obligations. The respective indemnities, agreements, representations, warranties and other statements of the Company or its officers and of the several Underwriters set forth in or made pursuant to this Agreement will remain in full force and effect, regardless of any investigation, or statement as to the results thereof, made by or on behalf of any Underwriter, the Company or any of their respective representatives, officers or directors or any controlling person, and will survive delivery of and payment for the Offered Securities. If this Agreement is terminated pursuant to Section 8 or if for any reason the purchase of the Offered Securities by the Underwriters is not consummated, the Company shall remain responsible for the expenses to be paid or reimbursed by it pursuant to Section 5 and the respective obligations of the Company and the Underwriters pursuant to Section 7 shall remain in effect, and if any Offered Securities have been purchased hereunder the representations and warranties in Section 2 and all obligations under Section 5 shall also remain in effect. If the purchase of the Offered Securities by the Underwriters is not consummated for any reason other than solely because of the termination of this Agreement pursuant to Section 8 or the occurrence of any event

specified in clause (iii), (iv), (v), (vi) or (vii) of Section 6(c), the Company will reimburse the Underwriters for all out-of-pocket expenses (including reasonable fees and disbursements of counsel) reasonably incurred by them in connection with the offering of the Offered Securities.

10. Notices. All communications hereunder will be in writing and, if sent to the Underwriters, will be mailed, delivered or faxed and confirmed to the Representatives, c/o Lehman Brothers Inc., 745 7^th Avenue, New York, New York 10019, Attention: Debt Capital Markets, Financial Institutions Group; fax number (212) 526-0943, with a copy to the General Counsel at the same address, or, if sent to the Company, will be mailed, delivered or faxed and confirmed to it at Washington Mutual, Inc., 1202 Third Avenue, Seattle, WA 98103, Attention: Fay Chapman (fax: 206-461-5739) with a copy to David R. Wilson, Heller Ehrman White & McAuliffe LLP, 701 5^th Avenue, Suite 6100, Seattle, WA 98104-7098 (fax: 206-447-0849); provided, however, that any notice to an Underwriter pursuant to Section 7 will be mailed, delivered or telegraphed and confirmed to such Underwriter.

11. Successors. This Agreement will inure to the benefit of and be binding upon the parties hereto and their respective successors and the officers and directors and controlling persons referred to in Section 7, and no other person will have any right or obligation hereunder.

12. Representation of Underwriters. The Representatives will act for the several Underwriters in connection with this financing, and any action under this Agreement taken by the Representatives jointly or severally will be binding upon all the Underwriters.

13. Counterparts. This Agreement may be executed in any number of counterparts, each of which shall be deemed to be an original, but all such counterparts shall together constitute one and the same Agreement.

14. Applicable Law. This Agreement shall be governed by, and construed in accordance with, the laws of the State of New York without regard to principles of conflicts of laws.

The Company hereby submits to the non-exclusive jurisdiction of the federal and state courts in the Borough of Manhattan in The City of New York in any suit or proceeding arising out of or relating to this Agreement or the transactions contemplated hereby.

If the foregoing is in accordance with the Representatives’ understanding of our agreement, kindly sign and return to the Company one of the counterparts hereof, whereupon it will become a binding agreement between the Company and the several Underwriters in accordance with its terms.

Very truly yours,

	WASHINGTON MUTUAL, INC.

		By	/s/ Thomas W. Casey
				Thomas W. Casey
				Chief Financial Officer

The foregoing Underwriting Agreement is hereby confirmed and accepted as of the date first above written.

LEHMAN BROTHERS INC.
MORGAN STANLEY & CO. INCORPORATED

Acting on behalf of themselves and as the Representatives of the several Underwriters

	By LEHMAN BROTHERS INC.


		By	/s/ John Jedlik
				Authorized Representative

SCHEDULE A

Underwriter	Principal Amount of 4.20% Notes		Principal Amount of Floating Rate Notes
Lehman Brothers Inc.	225,000,000		93,750,000
Morgan Stanley & Co. Incorporated	225,000,000		93,750,000
ABN AMRO Incorporated	26,400,000		11,000,000
Banc of America Securities LLC	26,400,000		11,000,000
BNY Capital Markets, Inc.	26,400,000		11,000,000
Credit Suisse First Boston LLC	26,400,000		11,000,000
Wachovia Securities, Inc.	26,400,000		11,000,000
International Strategy & Investment Group Inc.	6,000,000		2,500,000
Samuel A. Ramirez & Company, Inc.	6,000,000		2,500,000
The Williams Capital Group, LP	6,000,000		2,500,000
Total	$	600,000,000	$	250,000,000