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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C.  20549

FORM 10-Q

(Mark One)

Commission file number:  0-26456

ARCH CAPITAL GROUP LTD.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code:  (441) 278-9250

(Former name, former address and former fiscal year, if changed since last report)

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.   Yes x     No o

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See the definitions of “large accelerated filer,” “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act.

Indicate by check mark whether the Registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act).  Yes o     No x

Indicate the number of shares outstanding of each of the issuer’s classes of common shares as of the latest practicable date.

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ARCH CAPITAL GROUP LTD.

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Report of Independent Registered Public Accounting Firm

To the Board of Directors and Shareholders of

Arch Capital Group Ltd.:

We have reviewed the accompanying consolidated balance sheets of Arch Capital Group Ltd. and its subsidiaries (the “Company”) as of June 30, 2008, and the related consolidated statements of income for each of the three-month and six-month periods ended June 30, 2008 and June 30, 2007, and the consolidated statements of changes in shareholders’ equity, comprehensive income and cash flows for the six-month periods ended June 30, 2008 and June 30, 2007. These interim financial statements are the responsibility of the Company’s management.

We conducted our review in accordance with the standards of the Public Company Accounting Oversight Board (United States). A review of interim financial information consists principally of applying analytical procedures and making inquiries of persons responsible for financial and accounting matters. It is substantially less in scope than an audit conducted in accordance with the standards of the Public Company Accounting Oversight Board (United States), the objective of which is the expression of an opinion regarding the financial statements taken as a whole. Accordingly, we do not express such an opinion.

Based on our review, we are not aware of any material modifications that should be made to the accompanying consolidated interim financial statements for them to be in conformity with accounting principles generally accepted in the United States of America.

We previously audited, in accordance with the standards of the Public Company Accounting Oversight Board (United States), the consolidated balance sheet as of December 31, 2007, and the related consolidated statements of income, changes in shareholders’ equity, comprehensive income, and of cash flows for the year then ended (not presented herein), and in our report dated February 28, 2008, we expressed an unqualified opinion on those consolidated financial statements. In our opinion, the information set forth in the accompanying consolidated balance sheet information as of December 31, 2007, is fairly stated in all material respects in relation to the consolidated balance sheet from which it has been derived.

/s/ PricewaterhouseCoopers LLP

New York, New York

August 8, 2008

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ARCH CAPITAL GROUP LTD. AND SUBSIDIARIES

CONSOLIDATED BALANCE SHEETS

(U.S. dollars in thousands, except share data)

See Notes to Consolidated Financial Statements

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CONSOLIDATED STATEMENTS OF INCOME

(U.S. dollars in thousands, except share data)

See Notes to Consolidated Financial Statements

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CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS’ EQUITY

(U.S. dollars in thousands)

See Notes to Consolidated Financial Statements

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CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME

(U.S. dollars in thousands)

See Notes to Consolidated Financial Statements

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CONSOLIDATED STATEMENTS OF CASH FLOWS

(U.S. dollars in thousands)

See Notes to Consolidated Financial Statements

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ARCH CAPITAL GROUP LTD. AND SUBSIDIARIES

NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (UNAUDITED)

1.      General

Arch Capital Group Ltd. (“ACGL”) is a Bermuda public limited liability company which provides insurance and reinsurance on a worldwide basis through its wholly owned subsidiaries.

The interim consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of ACGL and its wholly owned subsidiaries (together with ACGL, the “Company”). All significant intercompany transactions and balances have been eliminated in consolidation. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates and assumptions. In the opinion of management, the accompanying unaudited interim consolidated financial statements reflect all adjustments (consisting of normal recurring accruals) necessary for a fair statement of results on an interim basis. The results of any interim period are not necessarily indicative of the results for a full year or any future periods.

Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted; however, management believes that the disclosures are adequate to make the information presented not misleading. This report should be read in conjunction with the Company’s Annual Report on Form 10-K for the year ended December 31, 2007, including the Company’s audited consolidated financial statements and related notes and the section entitled “Risk Factors.”

To facilitate period-to-period comparisons, certain amounts in the 2007 consolidated financial statements have been reclassified to conform to the 2008 presentation. Such reclassifications had no effect on the Company’s consolidated net income. Tabular dollars and share amounts are in thousands, except per share amounts.

2.      Share Transactions

Share Repurchase Program

The board of directors of ACGL has authorized the investment of up to $1.5 billion in ACGL’s common shares through a share repurchase program. Such amount consisted of a $1.0 billion authorization in February 2007 and a $500 million authorization in May 2008. Repurchases under the program may be effected from time to time in open market or privately negotiated transactions through February 2010. Since the inception of the share repurchase program, ACGL has repurchased approximately 13.4 million common shares for an aggregate purchase price of $926.8 million. During the 2008 second quarter and six months ended June 30, 2008, ACGL repurchased approximately 2.9 million and 5.6 million common shares, respectively, for an aggregate purchase price of $199.9 million and $389.8 million, respectively. As a result of share repurchase transactions, book value per common share was reduced by $2.09 per share at June 30, 2008. Weighted average shares outstanding for the 2008 second quarter and six months ended June 30, 2008 were reduced by 11.9 million and 10.6 million shares, respectively. Weighted average shares outstanding for the 2007 second quarter and six months ended June 30, 2007 were reduced by 1.8 million and 1.0 million shares, respectively.

The timing and amount of the repurchase transactions under this program will depend on a variety of factors, including market conditions and corporate and regulatory considerations. In connection with the repurchase program, the Warburg Pincus funds waived their rights relating to share repurchases under its shareholders agreement with ACGL for all repurchases of common shares by ACGL under the repurchase program in open market transactions and certain privately negotiated transactions.

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NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (UNAUDITED)

Non-Cumulative Preferred Shares

During 2006, ACGL completed two public offerings of non-cumulative preferred shares (“Preferred Shares”). On February 1, 2006, $200.0 million principal amount of 8.0% series A non-cumulative preferred shares (“Series A Preferred Shares”) were issued with net proceeds of $193.5 million and, on May 24, 2006, $125.0 million principal amount of 7.875% series B non-cumulative preferred shares (“Series B Preferred Shares”) were issued with net proceeds of $120.9 million. The net proceeds of the offerings were used to support the underwriting activities of ACGL’s insurance and reinsurance subsidiaries. ACGL has the right to redeem all or a portion of each series of Preferred Shares at a redemption price of $25.00 per share on or after (1) February 1, 2011 for the Series A Preferred Shares and (2) May 15, 2011 for the Series B Preferred Shares. Dividends on the Preferred Shares are non-cumulative. Consequently, in the event dividends are not declared on the Preferred Shares for any dividend period, holders of Preferred Shares will not be entitled to receive a dividend for such period, and such undeclared dividend will not accrue and will not be payable. Holders of Preferred Shares will be entitled to receive dividend payments only when, as and if declared by ACGL’s board of directors or a duly authorized committee of the board of directors. Any such dividends will be payable from the date of original issue on a non-cumulative basis, quarterly in arrears. To the extent declared, these dividends will accumulate, with respect to each dividend period, in an amount per share equal to 8.0% of the $25.00 liquidation preference per annum for the Series A Preferred Shares and 7.875% of the $25.00 liquidation preference per annum for the Series B Preferred Shares. At June 30, 2008, the Company had declared an aggregate of $3.3 million of dividends to be paid to holders of the Preferred Shares.

Share-Based Compensation

As required by the provisions of Financial Accounting Standards Board (“FASB”) Statement No. 123 (revised 2004), “Share-Based Payment” (“SFAS No. 123(R)”), the Company recorded after-tax share-based compensation expense related to stock options in the 2008 second quarter of $2.8 million, or $0.04 per diluted share, compared to $2.8 million, or $0.04 per diluted share, in the 2007 second quarter, and $3.9 million, or $0.06 per diluted share, for the six months ended June 30, 2008, compared to $4.4 million, or $0.06 per diluted share, for the six months ended June 30, 2007.

During the 2008 second quarter, the Company made a stock grant of 333,175 stock appreciation rights and stock options and 328,575 restricted shares and units to certain employees. The stock appreciation rights and stock options were valued at the grant date using the Black-Scholes option pricing model. The weighted average grant-date fair value of the stock appreciation rights and options and restricted shares and units granted were approximately $19.07 and $69.30 per share, respectively. Such value will be amortized over the respective substantive vesting period.

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3.      Debt and Financing Arrangements

Senior Notes

On May 4, 2004, ACGL completed a public offering of $300 million principal amount of 7.35% senior notes (“Senior Notes”) due May 1, 2034 and received net proceeds of $296.4 million. ACGL used $200 million of the net proceeds to repay all amounts outstanding under a revolving credit agreement. The Senior Notes are ACGL’s senior unsecured obligations and rank equally with all of its existing and future senior unsecured indebtedness. Interest payments on the Senior Notes are due on May 1st and November 1st of each year. ACGL may redeem the Senior Notes at any time and from time to time, in whole or in part, at a “make-whole” redemption price. For the six months ended June 30, 2008 and 2007, interest expense on the Senior Notes was approximately $11.0 million. The fair value of the Senior Notes at June 30, 2008 and December 31, 2007 was $304.1 million and $325.4 million, respectively.

Letter of Credit and Revolving Credit Facilities

As of June 30, 2008, the Company had a $300 million unsecured revolving loan and letter of credit facility and a $1.0 billion secured letter of credit facility (the “Credit Agreement”). The $300 million unsecured revolving loan is also available for the issuance of unsecured letters of credit up to $100 million for Arch Reinsurance Company (“Arch Re U.S.”). Borrowings of revolving loans may be made by ACGL and Arch Re U.S. at a variable rate based on LIBOR or an alternative base rate at the option of the Company. Secured letters of credit are available for issuance on behalf of the Company’s insurance and reinsurance subsidiaries. Issuance of letters of credit and borrowings under the Credit Agreement are subject to the Company’s compliance with certain covenants and conditions, including absence of a material adverse change. These covenants require, among other things, that the Company maintain a debt to shareholders’ equity ratio of not greater than 0.35 to 1 and shareholders’ equity in excess of $1.95 billion plus 25% of future aggregate net income for each quarterly period (not including any future net losses) beginning after June 30, 2006 and 25% of future aggregate proceeds from the issuance of common or preferred equity and that the Company’s principal insurance and reinsurance subsidiaries maintain at least a “B++” rating from A.M. Best. In addition, certain of the Company’s subsidiaries which are party to the Credit Agreement are required to maintain minimum shareholders’ equity levels. The Company was in compliance with all covenants contained in the Credit Agreement at June 30, 2008. The Credit Agreement expires on August 30, 2011.

In May 2008, the Company borrowed $100.0 million under the Credit Agreement at a variable interest rate based on 1 month, 3 month or 6 month LIBOR rates plus 27.5 basis points. The proceeds from such borrowings, which are repayable on August 30, 2011, were contributed to Arch Reinsurance Ltd. (“Arch Re Bermuda”) and used to fund an investment in a joint venture. See Note 6, “Investment Information—Investment in Joint Venture.” The Company incurred interest expense in connection with the borrowing of $0.3 million during the 2008 second quarter.

Including the secured letter of credit portion of the Credit Agreement and another letter of credit facility (together, the “LOC Facilities”), the Company has access to letter of credit facilities for up to a total of $1.45 billion. The principal purpose of the LOC Facilities is to issue, as required, evergreen standby letters of credit in favor of primary insurance or reinsurance counterparties with which the Company has entered into reinsurance arrangements to ensure that such counterparties are permitted to take credit for reinsurance obtained from the Company’s reinsurance subsidiaries in United States jurisdictions where such subsidiaries are not licensed or otherwise admitted as an insurer, as required under insurance regulations in the United States, and to comply with requirements of Lloyd’s of London in connection with qualifying quota share and other arrangements. The amount of letters of credit issued is driven by, among other things, the timing and payment of catastrophe losses, loss development of existing reserves, the payment pattern of such reserves, the further expansion of the Company’s business and the loss experience of such business. When issued, certain letters of credit are secured by a portion of the Company’s investment portfolio. In addition, the LOC Facilities also require the maintenance

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NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (UNAUDITED)

of certain covenants, which the Company was in compliance with at June 30, 2008. At such date, the Company had approximately $565.0 million in outstanding letters of credit under the LOC Facilities, which were secured by investments totaling $582.2 million at fair value. It is anticipated that the LOC Facilities will be renewed (or replaced) on expiry, but such renewal (or replacement) will be subject to the availability of credit from banks which the Company utilizes. In addition to letters of credit, the Company has and may establish insurance trust accounts in the U.S. and Canada to secure its reinsurance amounts payable as required.

4.      Segment Information

The Company classifies its businesses into two underwriting segments — insurance and reinsurance — and corporate and other (non-underwriting). The Company’s insurance and reinsurance operating segments each have segment managers who are responsible for the overall profitability of their respective segments and who are directly accountable to the Company’s chief operating decision makers, the President and Chief Executive Officer of ACGL and the Chief Financial Officer of ACGL. The chief operating decision makers do not assess performance, measure return on equity or make resource allocation decisions on a line of business basis. The Company determined its reportable operating segments using the management approach described in SFAS No. 131, “Disclosures about Segments of an Enterprise and Related Information.”

Management measures segment performance based on underwriting income or loss. The Company does not manage its assets by segment and, accordingly, investment income is not allocated to each underwriting segment. In addition, other revenue and expense items are not evaluated by segment. The accounting policies of the segments are the same as those used for the preparation of the Company’s consolidated financial statements. Intersegment business is allocated to the segment accountable for the underwriting results.

The insurance segment consists of the Company’s insurance underwriting subsidiaries which primarily write on both an admitted and non-admitted basis. The insurance segment consists of nine product lines: casualty; construction and national accounts; executive assurance; healthcare; professional liability; programs; property, marine and aviation; surety; and other (consisting of collateral protection, excess workers’ compensation and employers’ liability business and travel and accident business).

The reinsurance segment consists of the Company’s reinsurance underwriting subsidiaries. The reinsurance segment generally seeks to write significant lines on specialty property and casualty reinsurance treaties. Classes of business include: casualty; marine and aviation; other specialty; property catastrophe; property excluding property catastrophe (losses on a single risk, both excess of loss and pro rata); and other (consisting of non-traditional and casualty clash business).

Corporate and other (non-underwriting) includes net investment income, other fee income, net of related expenses, other income (loss), other expenses incurred by the Company, interest expense, net realized gains or losses, equity in net income (loss) of investment funds accounted for using the equity method, net foreign exchange gains or losses and income taxes. In addition, corporate and other results include dividends on the Company’s non-cumulative preferred shares.

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NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (UNAUDITED)

The following tables set forth an analysis of the Company’s underwriting income by segment, together with a reconciliation of underwriting income to net income available to common shareholders:

(1)         Certain amounts included in the gross premiums written of each segment are related to intersegment transactions. Accordingly, the sum of gross premiums written for each segment does not agree to the total gross premiums written as shown in the table above due to the elimination of intersegment transactions in the total. The insurance segment and reinsurance segment results include $0.1 million and $8.0 million, respectively, of gross and net premiums written and $0.1 million and $8.5 million, respectively, of net premiums earned assumed through intersegment transactions.

(2)         The acquisition expense ratio is adjusted to include policy-related fee income.

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(1)         Certain amounts included in the gross premiums written of each segment are related to intersegment transactions. Accordingly, the sum of gross premiums written for each segment does not agree to the total gross premiums written as shown in the table above due to the elimination of intersegment transactions in the total. The insurance segment and reinsurance segment results include $0.3 million and $9.6 million, respectively, of gross and net premiums written and $0.3 million and $10.8 million, respectively, of net premiums earned assumed through intersegment transactions.

(2)         The acquisition expense ratio is adjusted to include policy-related fee income.

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