Table of Contents

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-K

ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the fiscal year ended December 31, 2010

Commission File No. 1-5998

Marsh & McLennan Companies, Inc.

(Exact name of registrant as specified in its charter)

1166 Avenue of the Americas

New York, New York 10036-2774

(Address of principal executive offices; Zip Code)

(212) 345-5000

Registrant’s telephone number, including area code

Securities registered pursuant to Section 12(b) of the Act:

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. Yes x. No ¨.

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Act. Yes ¨. No x.

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 ¨.

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K is not contained herein, and will not be contained, to the best of registrant’s knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K. ¨.

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Website, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files). Yes x. No¨.

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 definitions of “large accelerated filer,” “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act (check one).

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

As of June 30, 2010, the aggregate market value of the registrant’s common stock held by non-affiliates of the registrant was approximately $12,195,379,683, computed by reference to the closing price of such stock as reported on the New York Stock Exchange on June 30, 2010.

As of February 18, 2011, there were outstanding 544,088,185 shares of common stock, par value $1.00 per share, of the registrant.

DOCUMENTS INCORPORATED BY REFERENCE

Portions of Marsh & McLennan Companies, Inc.’s Notice of Annual Meeting and Proxy Statement for the 2011 Annual Meeting of Stockholders (the “2011 Proxy Statement”) are incorporated by reference in Part III of this Form 10-K.

Table of Contents

INFORMATION CONCERNING FORWARD-LOOKING STATEMENTS

This Annual Report on Form 10-K contains “forward-looking statements,” as defined in the Private Securities Litigation Reform Act of 1995. These statements, which express management’s current views concerning future events or results, use words like “anticipate,” “assume,” “believe,” “continue,” “estimate,” “expect,” “future,” “intend,” “plan,” “project” and similar terms, and future or conditional tense verbs like “could,” “may,” “might,” “should,” “will” and “would.” For example, we may use forward-looking statements when addressing topics such as: the outcome of contingencies; market and industry conditions; changes in our business strategies and methods of generating revenue; the development and performance of our services and products; changes in the composition or level of our revenues; our cost structure and the outcome of cost-saving or restructuring initiatives; dividend policy; the expected impact of acquisitions and dispositions; pension obligations; cash flow and liquidity; future actions by regulators; and the impact of changes in accounting rules.

Forward-looking statements are subject to inherent risks and uncertainties. Factors that could cause actual results to differ materially from those expressed or implied in our forward-looking statements include, among other things:

The factors identified above are not exhaustive. Marsh & McLennan Companies and its subsidiaries operate in a dynamic business environment in which new risks may emerge frequently. Accordingly, we caution readers not to place undue reliance on the above forward-looking statements, which speak only as of the dates on which they are made. The Company undertakes no obligation to update or revise any forward-looking statement to reflect events or circumstances arising after the date on which

i

Table of Contents

it is made. Further information concerning the Company and its businesses, including information about factors that could materially affect our results of operations and financial condition, is contained in the Company’s filings with the Securities and Exchange Commission, including the “Risk Factors” section in Part I, Item 1A of this report.

ii

Table of Contents

Table of Contents

iii

Table of Contents

MARSH & McLENNAN COMPANIES, INC.

ANNUAL REPORT ON FORM 10-K

FOR THE YEAR ENDED DECEMBER 31, 2010

PART I

ITEM 1.      BUSINESS.

References in this report to “we”, “us” and “our” are to Marsh & McLennan Companies, Inc. (the “Company”) and one or more of its subsidiaries, as the context requires.

GENERAL

The Company is a global professional services firm providing advice and solutions in the areas of risk, strategy and human capital. It is the parent company of a number of the world’s leading risk experts and specialty consultants, including: Marsh, the insurance broker, intermediary and risk advisor; Guy Carpenter, the risk and reinsurance specialist; Mercer, the provider of HR and related financial advice and services; and Oliver Wyman Group, the management and economic consultancy. With approximately 51,000 employees worldwide and annual revenue exceeding $10 billion, the Company provides analysis, advice and transactional capabilities to clients in more than 100 countries.

The Company conducts business through two operating segments:

On August 3, 2010, the Company completed the sale of 100% of the issued and outstanding shares of the Company’s indirect wholly-owned subsidiary, Kroll Inc. (“Kroll”) pursuant to a definitive Stock Purchase Agreement with Altegrity, Inc., a portfolio company of Providence Equity Partners. Kroll previously constituted the Company’s Risk Consulting and Technology segment.

We describe our current operating segments in further detail below. We provide financial information about our segments in our consolidated financial statements included under Part II, Item 8 of this report.

OUR BUSINESSES

RISK AND INSURANCE SERVICES

The Risk and Insurance Services segment generated approximately 54% of the Company’s total operating segment revenue in 2010 and employs approximately 27,000 colleagues worldwide. The Company conducts business in this segment through Marsh and Guy Carpenter.

MARSH

Marsh is a world leader in delivering risk and insurance services and solutions to its clients. From its founding in 1871 to the present day, Marsh has provided thought leadership and innovation for clients and the insurance industry—introducing and promoting the concept and practice of client representation through brokerage, the discipline of risk management, the globalization of insurance and risk management services and many other innovative tools and service platforms.

1

Table of Contents

Marsh generated approximately 45% of the Company’s total operating segment revenue in 2010. Nearly 25,000 Marsh colleagues provide risk management, risk consulting, insurance broking, alternative risk financing, and insurance program management services to a wide range of businesses, government entities and professional service organizations around the world in more than 100 countries.

Marsh’s clients vary by size, industry, geography and risk exposures. Marsh is organized to serve clients efficiently and effectively, delivering tailored solutions based on complexity of the risk and global footprint, and matched to clients’ buying styles.

Insurance Broking and Risk Consulting

In its main insurance broking and risk consulting business, Marsh employs a team approach to address clients’ risk management and insurance needs. Each client relationship is coordinated by a client executive who draws from the many industry and risk specialties within Marsh to assemble the resources needed to analyze, measure and assist a client in managing its various risks. Product and service offerings include program design and placement, post-placement program support and administration, claims advocacy, and a wide array of risk analysis and risk management consulting services. Within Marsh, there are several significant specialties or businesses in addition to our brokerage operations that serve as an important part of the overall capabilities we offer clients. These include Multinational Client Service, Marsh Risk Consulting, Risk, Specialty and Industry Practices, Bowring Marsh, Consumer Operations, Marsh & McLennan Agency, Captive Solutions, Schinnerer Group and Marsh Client Technologies.

Multinational Client Service

Multinational Client Service (MCS) is solely focused on delivering service excellence and insurance solutions to multinational clients, irrespective of their size. MCS provides risk management programs with a service platform that comprises a combination of proprietary tools and technology and specialized resources. MCS provides global expertise and an intimate knowledge of local markets, helping clients navigate local regulatory and legal environments and address the worldwide risk issues that confront them.

Marsh Risk Consulting

Marsh Risk Consulting (MRC) is a global organization comprised of consulting specialists dedicated to providing clients with advice and solutions across a comprehensive range of insurable and non-insurable risk issues, such as restructuring, product safety, patient safety, business interruption, supply chain, governance, workforce, and reputation. MRC helps clients identify exposures, assess critical business functions and evaluate existing risk treatment practices and strategies. MRC provides client services in five main areas of exposure:

2

Table of Contents

Risk, Specialty and Industry Practices

In further support of its clients’ strategic, operational and risk management objectives, Marsh provides consultative advice, brokerage and claims advocacy services through dedicated global Risk, Specialty and Industry Practices in the areas listed below. For both large and mid-size organizations, Practice colleagues apply their experience and working knowledge of clients’ industry sectors, and of the unique environments in which they operate, to facilitate the requisite breadth of coverage and to reduce cost of risk.

Bowring Marsh

Bowring Marsh was established in 2008 to respond to clients’ growing needs and marketplace opportunity, specializing as an international placement broker for property (including terrorism) and casualty risks. Bowring Marsh utilizes placement expertise in major international insurance market hubs (including Bermuda, Brazil, Dublin, London, Miami, Singapore, Tokyo and Zurich) and an integrated global network to secure advantageous terms and conditions for its clients throughout the world.

Consumer Operations—Affinity/Program & Private Client

In addition to its main risk management and broking practices described above, Marsh operates a “Consumer” business in each geographic region that focuses on either or both of program marketing

3

Table of Contents

and administration opportunities and high net worth individual insurance sales. The Affinity/Program businesses sell and administer insurance products and services on a program basis, typically working with a sponsoring organization client to leverage the affinity relationship that client has with its constituencies (e.g., employees, members, franchisees, or customers, as the case may be). These programs typically include group life & health coverage, professional liability coverage, personal property and liability coverage including automobile and homeowners’ insurance, business owner protection, annuities, and variable security-related products. Marsh Consumer’s sales and servicing activities regarding high net worth individuals are largely U.S.-focused and operate under the names “Private Client Services” (for property & casualty insurance products), and “Private Client Life Insurance Solutions” or “Private Client Solutions” (for life & health insurance-focused activities).

More specifically, areas of the Consumer business include:

Marsh & McLennan Agency

In October 2008, Marsh established the Marsh & McLennan Agency (MMA) to be one of the premier insurance agencies in the United States, meeting the needs of mid-sized businesses across the country. MMA’s services are targeted to customers who seek professional advice on program structure, market knowledge, experience and expertise in their industry, competitive prices, and local resources and service professionals. MMA offers commercial property and casualty, personal lines, employee benefits and life insurance / estate planning to clients through a dedicated sales and service force in retail locations, operating independently from Marsh’s other insurance broking operations.

Captive Solutions

Operating in 33 captive domiciles, along with consulting expertise residing in Marsh brokerage offices worldwide, the Captive Solutions Practice serves approximately 1,277 captive facilities, including single-parent captives, reinsurance pools, risk retention groups and others. The Practice includes the Captive Advisory group—a consulting arm that performs captive feasibility studies and helps to structure and implement captive solutions and Captive Management— an industry leader in managing captive facilities and in providing administrative, consultative and insurance-related services.

Schinnerer Group

As one of the largest underwriting managers of professional liability and specialty insurance programs in the United States, Victor O. Schinnerer provides risk management and insurance solutions to clients through licensed brokers.

This group includes ENCON Group Inc., a leading managing general agent in Canada. ENCON offers professional liability and construction insurance, as well as group and retiree benefits programs for individuals, professionals, organizations and businesses, through a national network of licensed insurance brokers and plan advisors.

4

Table of Contents

Marsh Client Technologies

Marsh Client Technologies comprises MarshConnect, Marsh’s global client technology interface, and CS STARS, a leading provider of risk and claims management systems and related data services.

MarshConnect is a shared platform that delivers two sets of functions: Risk and Insurance Databases and Client Servicing Applications. Proprietary databases provide a broad range of risk and insurance market intelligence, research tools and interactive utilities. Additionally, MarshConnect offers real-time access to critical risk and insurance information relevant to a client’s operations and risk profile. The platform enables teams to share information, collaborate and transact business online, increasing operational efficiency for Risk Management departments.

CS STARS serves the technology needs of risk management professionals, as well as insurance carriers and third-party administrators, through integrated software and services that support risk management, claims administration, compliance management, and data management.

GUY CARPENTER

Guy Carpenter generated approximately 9% of the Company’s total operating segment revenue in 2010. Over 2,000 Guy Carpenter professionals create and execute reinsurance and risk management solutions for clients worldwide, by providing risk assessment analytics, actuarial services, highly specialized product knowledge and trading relationships with reinsurance markets. Client services also include contract and claims management and fiduciary accounting.

Acting as a broker or intermediary on all classes of reinsurance, Guy Carpenter places two main types of property and casualty reinsurance: treaty reinsurance, which involves the transfer of a portfolio of risks; and facultative reinsurance, which entails the transfer of part or all of the coverage provided by a single insurance policy.

Guy Carpenter also provides reinsurance services in a broad range of specialty practice areas, including: agriculture; alternative risk transfer (such as group-based captives and insurance pools); aviation & aerospace; casualty clash (losses involving multiple policies or insureds); construction and engineering; credit, bond & political risk; excess & umbrella; general casualty; life, accident & health; marine and energy; medical professional liability; professional liability; program manager solutions; property; retrocessional reinsurance (reinsurance between reinsurers); surety (reinsurance of surety bonds and other financial guarantees); terror risk and workers compensation.

Guy Carpenter also offers clients alternatives to traditional reinsurance, including industry loss warranties and, through its affiliates, capital markets alternatives such as transferring catastrophe risk through the issuance of risk-linked securities. GC Securities, the Guy Carpenter division of MMC Securities Corp., offers corporate finance solutions, including mergers & acquisitions and private debt and equity capital raising, and capital markets-based risk transfer solutions that complement Guy Carpenter’s strong industry relationships, analytical capabilities and reinsurance expertise.

In addition, Guy Carpenter provides its clients with numerous reinsurance-related services, such as actuarial, enterprise risk management, financial and regulatory consulting, portfolio analysis and advice on the efficient use of capital. Guy Carpenter’s GC Analytics™ unit serves as a local resource that helps clients better understand and quantify the uncertainties inherent in their businesses. Working in close partnership with Guy Carpenter account executives, GC Analytics specialists can help support clients’ critical decisions in numerous areas, including reinsurance utilization, catastrophe exposure portfolio management, new product/market development, rating agency, regulatory and account impacts, loss reserve risk, capital adequacy and return on capital.

Compensation for Services in Risk and Insurance Services

Marsh and Guy Carpenter are compensated for brokerage and consulting services primarily through fees and commissions. Commission rates vary in amount depending upon the type of insurance or reinsurance coverage provided, the particular insurer or reinsurer selected, the capacity in which the broker acts and negotiations with clients. Marsh and Guy Carpenter receive interest income on certain funds (such as premiums and claims proceeds) held in a fiduciary capacity for others.

5

Table of Contents

For a more detailed discussion of revenue sources and factors affecting revenue in our Risk and Insurance Services segment, see Part II, Item 7 (“Management’s Discussion and Analysis of Financial Condition and Results of Operations”) of this report.

CONSULTING

The Company’s consulting segment generated approximately 46% of total operating segment revenue in 2010 and employs approximately 23,000 colleagues worldwide. The Company conducts business in this segment through Mercer and Oliver Wyman Group.

MERCER

With nearly 20,000 professionals active in 41 countries, Mercer is a leading global provider of human resource consulting and related outsourcing and investment services. Clients include a majority of the companies in the Fortune 1000 and FTSE 100, as well as medium- and small-market organizations. Mercer generated approximately 33% of the Company’s total operating segment revenue in 2010.

Mercer operates in the following areas:

Retirement, Risk & Finance Consulting.  Mercer provides a wide range of strategic and compliance-related retirement services and solutions to corporate, governmental and institutional clients. Mercer assists clients worldwide in the design, governance and risk management of defined benefit, defined contribution and hybrid retirement plans. Mercer’s financial approach to retirement services enables clients to consider the benefits, accounting, funding and investment aspects of plan design and management in the context of business objectives and governance requirements.

Health & Benefits.  In its health & benefits business, Mercer assists public and private sector employers in the design, management and administration of employee health care programs; compliance with local benefits-related regulations; and the establishment of health and welfare benefits coverage for employees. Mercer provides advice and solutions to employers on: total health management strategies; global health brokerage solutions; vendor performance and audit; life and disability management; and measurement of healthcare provider performance. These services are provided through traditional consulting as well as commission-based brokerage services in connection with the selection of insurance companies and healthcare providers.

Rewards, Talent & Communications.  Mercer’s rewards, talent and communications businesses advise organizations on the engagement, management and rewarding of employees; the design of executive remuneration programs; and improvement of human resource (HR) effectiveness.

Through proprietary survey data and decision support tools, Mercer’s information products solutions business provides clients with human capital information and analytical capabilities to improve strategic human capital decision making.

Mercer’s communication business helps clients to plan and implement HR programs and other organizational changes in order to maximize employee engagement, drive desired employee behaviors and achieve improvements in business performance.

Outsourcing.  Through its outsourcing business, Mercer provides benefits administration services to clients globally. By delivering services across benefit domains and international borders, Mercer helps clients more efficiently manage their employee benefits programs. Mercer’s outsourcing business offers total benefits outsourcing, including administration and delivery for wealth, health and flexible benefits; total retirement outsourcing, including administration and delivery for retirement benefits; and stand-alone services for defined benefit administration, defined contribution administration, health benefits administration and flexible benefits programs.

Investment Consulting & Management.  Mercer provides investment consulting services to the fiduciaries of pension funds, foundations, endowments and other investors in more than 35 countries. Mercer advises clients and provides outsourced decision-making services covering all stages of the institutional investment process, from strategy, structure and implementation to ongoing portfolio management.

6

Table of Contents

Mercer’s investment management business provides multi-manager investment solutions, primarily for retirement plan assets, to institutional investors (such as retirement plan sponsors and trustees), and to individual investors (primarily through the inclusion of funds managed by Mercer on affiliated and third party defined contribution and financial advice platforms). These solutions include “one-stop” investment advisory and asset management solutions for plan sponsors, bundled services for frozen defined benefit plans utilizing our expertise in liability-driven investment and actuarial techniques, and personal wealth solutions. The investment management business offers a diverse range of investment options to meet a full spectrum of risk/return preferences and manages investment vehicles across a range of investment strategies in four geographic regions (US, Canada, Europe and Australia/New Zealand). As of December 31, 2010, Mercer’s investment management business had assets under management and assets under advisory of $39.6 billion worldwide.

OLIVER WYMAN GROUP

With approximately 3,400 professionals based in 25 countries, Oliver Wyman Group delivers advisory services to clients through three operating units, each of which is a leader in its field: Oliver Wyman; Lippincott; and NERA Economic Consulting. Oliver Wyman Group generated approximately 13% of the Company’s total operating segment revenue in 2010.

Oliver Wyman is a leading global management consulting firm. Oliver Wyman’s consultants specialize by industry and functional area, allowing clients to benefit from both deep sector knowledge and specialized expertise in strategy, operations, risk management, organizational transformation, and leadership development. Industry groups include:

Oliver Wyman overlays its industry knowledge with expertise in the following functional specializations:

7

Table of Contents

Lippincott is a brand strategy and design consulting firm which advises corporations around the world in a variety of industries on corporate branding, identity and image. Lippincott has helped create some of the world’s most recognized brands.

NERA Economic Consulting provides economic analysis and advice to public and private entities to achieve practical solutions to highly complex business and legal issues arising from competition, regulation, public policy, strategy, finance and litigation. NERA professionals operate worldwide assisting clients including corporations, governments, law firms, regulatory agencies, trade associations, and international agencies. NERA’s specialized practice areas include: antitrust; securities; complex commercial litigation; energy; environmental economics; network industries; intellectual property; product liability and mass torts; and transfer pricing.

Compensation for Services in Consulting

Mercer and the Oliver Wyman Group businesses are compensated for advice and services primarily through fees paid by clients. Mercer’s health & benefits business is compensated through commissions from insurance companies for the placement of insurance contracts (comprising more than half of the revenue in the health & benefits business) and consulting fees. Mercer’s discretionary investment management business and certain of Mercer’s defined contribution administration services are compensated typically through fees based on assets under administration and/or management. For a more detailed discussion of revenue sources and factors affecting revenue in the Consulting segment, see Part II, Item 7 (“Management’s Discussion and Analysis of Financial Condition and Results of Operations”) of this report.

REGULATION

The Company’s activities are subject to licensing requirements and extensive regulation under United States federal and state laws, as well as laws of other countries in which the Company’s subsidiaries operate. See Part I, Item 1A (“Risk Factors”) below for a discussion of how actions by regulatory authorities or changes in legislation and regulation in the jurisdictions in which we operate may have an adverse effect on our businesses.

Risk and Insurance Services.  While laws and regulations vary from location to location, every state of the United States and most foreign jurisdictions require insurance market intermediaries and related service providers (such as insurance brokers, agents and consultants, reinsurance brokers, managing general agents and third party administrators) to hold an individual and/or company license from a governmental agency or self-regulatory organization. Some jurisdictions issue licenses only to individual residents or locally-owned business entities; in this case, if the Company has no licensed subsidiary, we may maintain arrangements with residents or business entities licensed to act in such jurisdiction. Such arrangements are only permitted following an extensive review process.

8

Table of Contents

Beginning in January 2005, all European Union member states were required to implement the Insurance Mediation Directive. This Directive aims to apply consistent minimum professional standards to insurance and reinsurance intermediaries, including a licensing system based on an assessment of factors such as professional competence, financial capacity and professional indemnity insurance. The adoption by member states of the European Union of regulations to comply with the Directive has led our insurance intermediary operations in the European Union to become subject to enhanced regulatory requirements. In January 2005, as part of the implementation of the Directive in the United Kingdom, the power and responsibilities of the Financial Services Authority, or FSA, were expanded to include regulation of insurance and reinsurance intermediaries in the United Kingdom.

Insurance authorities in the United States and certain other jurisdictions in which the Company’s subsidiaries do business, including the FSA in the United Kingdom, also have enacted laws and regulations governing the investment of funds, such as premiums and claims proceeds, held in a fiduciary capacity for others. These laws and regulations typically provide for segregation of these fiduciary funds and limit the types of investments that may be made with them.

Certain of the Company’s Risk and Insurance Services activities are governed by other regulatory bodies, such as investment, securities and futures licensing authorities. In the United States, Marsh and Guy Carpenter use the services of MMC Securities Corp., a broker-dealer and investment adviser, registered in the U.S. with the SEC, and a member of the Financial Industry Regulatory Agency (FINRA) and the Securities Investor Protection Corporation (SIPC), primarily in connection with investment banking-related services relating to insurance-linked and alternative risk financing transactions. Also in the United States, Marsh uses the services of NIA Securities, LLC, a U.S. registered broker-dealer and investment adviser. Guy Carpenter provides advice on securities or investments in the European Union through MMC Securities (Europe) Limited, which is authorized and regulated by the FSA. Marsh also receives investment management services in the European Union from Marsh Investment Service Limited, which is also regulated by the FSA. MMC Securities Corp., MMC Securities (Europe) Limited, NIA Securities, LLC, and Marsh Investment Service Limited are indirect, wholly-owned subsidiaries of Marsh & McLennan Companies.

In some jurisdictions, insurance-related taxes may be due either directly from clients or from the insurance broker. In the latter case, the broker customarily looks to the client for payment.

Consulting.  Certain of Mercer’s retirement-related consulting services are subject to pension law and financial regulation in many countries, including by the SEC in the United States and the FSA in the United Kingdom. In addition, the trustee services, investment services (including advice to persons, institutions and other entities on the investment of pension assets and assumption of discretionary investment management responsibilities) and retirement and employee benefit program administrative services provided by Mercer and its subsidiaries and affiliates are subject to investment and securities regulations in various jurisdictions. The benefits insurance consulting and brokerage services provided by Mercer and its subsidiaries and affiliates are subject to the same licensing requirements and regulatory oversight as the insurance market intermediaries described above regarding our Risk and Insurance Services businesses. Mercer uses the services of MMC Securities Corp. with the provision of certain retirement and employee benefit services. Oliver Wyman Group use the services of MMC Securities Corp. (in the United States) and MMC Securities (Europe) Limited (in the European Union), primarily in connection with corporate finance advisory services.

COMPETITIVE CONDITIONS

The Company faces strong competition in all of its businesses from providers of similar products and services, including competition with regard to identifying and pursuing acquisition candidates. The Company also encounters strong competition throughout its businesses from both public corporations and private firms in attracting and retaining qualified employees. In addition to the discussion below, see “Risks Relating to the Company Generally –Competitive Risks,” in Part I, Item 1A of this report.

Risk and Insurance Services.  The Company’s combined insurance and reinsurance services businesses are global in scope. The principal bases upon which our insurance and reinsurance

9

Table of Contents

businesses compete include the range, quality and cost of the services and products provided to clients. The Company encounters strong competition from other insurance and reinsurance brokerage firms that operate on a nationwide or worldwide basis, from a large number of regional and local firms in the United States, the European Union and elsewhere, from insurance and reinsurance companies that market, distribute and service their insurance and reinsurance products without the assistance of brokers or agents and from other businesses, including commercial and investment banks, accounting firms and consultants, that provide risk-related services and products.

Certain insureds and groups of insureds have established programs of self insurance (including captive insurance companies) as a supplement or alternative to third-party insurance, thereby reducing in some cases their need for insurance placements. Certain insureds also obtain coverage directly from insurance providers. There are also many other providers of affinity group and private client services, including specialized firms, insurance companies and other institutions.

The continuing impact of legal and regulatory proceedings concerning our insurance brokerage operations also could affect Marsh’s competitive position. These proceedings are discussed in more detail in Note 16 to the consolidated financial statements included under Part II, Item 8 of this report. Please also read our discussion of the risks associated with these proceedings and their impact under Part I, Item 1A (“Risk Factors”) below.

Consulting.  The Company’s consulting and HR outsourcing businesses face strong competition from other privately and publicly held worldwide and national companies, as well as regional and local firms. These businesses compete generally on the basis of the range, quality and cost of the services and products provided to clients. Competitors include independent consulting and outsourcing firms, as well as consulting and outsourcing operations affiliated with accounting, information systems, technology and financial services firms.

Mercer’s investment consulting and investment management businesses face competition from many sources, including multi-manager services offered by other investment consulting firms and financial institutions.

In many cases, clients have the option of handling the services provided by Mercer and Oliver Wyman Group internally, without assistance from outside advisors.

Segmentation of Activity by Type of Service and Geographic Area of Operation.

Financial information relating to the types of services provided by the Company and the geographic areas of its operations is incorporated herein by reference to Note 17 to the consolidated financial statements included under Part II, Item 8 of this report.

Employees

As of December 31, 2010, the Company and its consolidated subsidiaries employed approximately 51,000 people worldwide, including approximately 27,000 in risk and insurance services and approximately 23,000 in consulting. Approximately 1,000 individuals are employed by the Company at the parent-company level.

EXECUTIVE OFFICERS OF THE COMPANY

The executive officers of the Company are appointed annually by the Company’s Board of Directors. As of February 25, 2011, the following individuals were executive officers of the Company:

Orlando D. Ashford, age 42, is Senior Vice President, Human Resources, of Marsh & McLennan Companies. Mr. Ashford joined the Company in September 2008. Prior to Marsh & McLennan Companies, he was with the Coca-Cola Company since 2005 in human resource management, most recently as Group Director of Human Resources for Eurasia and Africa. While at Coca-Cola, Mr. Ashford reorganized and rebuilt the Company’s corporate center HR team and headed a company-wide cultural change initiative. Prior to Coca-Cola, Mr. Ashford held positions with Motorola, the Delta Consulting Group (subsequently Mercer Delta Consulting), Ameritech and Andersen Consulting.

10

Table of Contents

Peter J. Beshar, age 49, is Executive Vice President and General Counsel of Marsh & McLennan Companies. Before joining the Company in November 2004, Mr. Beshar was a Litigation Partner in the law firm of Gibson, Dunn & Crutcher LLP. Mr. Beshar joined Gibson, Dunn & Crutcher in 1995 after serving as an Assistant Attorney General in the New York Attorney General’s office and as the Special Assistant to Cyrus Vance in connection with the peace negotiations in the former Yugoslavia.

M. Michele Burns, age 52, is Chairman and Chief Executive Officer of Mercer. Ms. Burns joined the Company as Executive Vice President on March 1, 2006, assumed the position of Chief Financial Officer of Marsh & McLennan Companies on March 31, 2006 and moved to her current position with Mercer on September 25, 2006. Prior to joining the Company, Ms. Burns was Executive Vice President and Chief Financial Officer since May 2004, and Chief Restructuring Officer since August 2004, of Mirant Corporation, an energy company. Prior to joining Mirant, she was Executive Vice President and Chief Financial Officer of Delta Air Lines, Inc. from August 2000 to April 2004. She held various other positions in the finance and tax departments of Delta beginning in January 1999. Delta filed for protection under Chapter 11 of the United States Bankruptcy Code in September 2005.

John P. Drzik, age 48, is President and Chief Executive Officer of Oliver Wyman Group, a position he assumed in June 2006. From 2003 to 2006, Mr. Drzik was President of Mercer Oliver Wyman, which was formed following the Company’s acquisition of Oliver, Wyman & Company in 2003. He joined Oliver, Wyman & Company in 1984, became President in 1995, and was appointed Chairman in 2000.

Brian Duperreault, age 62, is Director, President and Chief Executive Officer of Marsh & McLennan Companies, a position he assumed in January 2008. Prior to joining the Company, Mr. Duperreault served as Chairman and Chief Executive Officer of ACE Limited from 1994 to 2004, and continued as Chairman through the end of 2007. Prior to ACE, Mr. Duperreault was with American International Group (AIG) for more than 20 years, holding numerous positions and eventually becoming Executive Vice President of AIG Foreign General Insurance and Chairman and Chief Executive of AIG’s American International Underwriters (AIU). Mr. Duperreault is a Director of Tyco International Ltd.

E. Scott Gilbert, age 55, is Senior Vice President and Chief Compliance Officer of Marsh & McLennan Companies. Prior to joining the Company in January 2005, he had been the Chief Compliance Counsel of the General Electric Company since September 2004. Prior thereto, he was Counsel, Litigation and Legal Policy at GE. Between 1986 and 1992, when he joined GE, he served as an Assistant United States Attorney for the Southern District of New York.

Daniel S. Glaser, age 50, is Chairman and Chief Executive Officer of Marsh, a position he assumed in December 2007. Previously, he had been Managing Director of AIG Europe (U.K.) Limited, and the Regional President of AIG’s American International Underwriters (AIU) U.K./Ireland division. He joined AIG in 2000 as President of the firm’s Global Energy Division. He was named Managing Director of AIG Europe (U.K.) in 2002. Mr. Glaser began his career in the insurance industry in 1982 as a Marsh broker. He worked at Marsh for a decade, serving in roles in New York, London and Saudi Arabia. Thereafter, he spent eight years at Willis, where he served as President and Chief Operating Officer of Willis Risk Solutions, the Willis large accounts practice.

David A. Nadler, age 62, is Vice Chairman, Office of the CEO of Marsh & McLennan Companies. Dr. Nadler founded the Delta Consulting Group, Inc., a consulting firm specializing in executive leadership and organizational change, in 1980. He served as Chairman and Chief Executive Officer of that firm until its acquisition by Mercer in 2000, when it became Mercer Delta Consulting. Dr. Nadler served as Chairman and Chief Executive Officer of Oliver Wyman’s Delta Organization & Leadership business through December 2005 and remains a Senior Partner of that firm.

Vanessa A. Wittman, age 43, is Executive Vice President and Chief Financial Officer of Marsh & McLennan Companies. Prior to joining the Company in September 2008, Ms. Wittman was Chief Financial Officer and Executive Vice President of Adelphia Communications Corp. from 2003 to 2007. She joined Adelphia as part of a new executive team that oversaw one of the most complex bankruptcy cases in U.S. history. While there, Ms. Wittman was responsible for accounting, tax and internal audit functions; operational and field finance; corporate development; and the bankruptcy and investor relations teams. Prior to Adelphia, Ms. Wittman served as Chief Financial Officer of 360networks,

11

Table of Contents

based in Seattle, where she led the Company’s restructuring efforts and successful emergence from bankruptcy protection in November 2002. She also has held positions with Microsoft, Metricom Inc. and Morgan Stanley.

Peter Zaffino, age 44, is President and Chief Executive Officer of Guy Carpenter. Prior to assuming this position in February 2008, he was an Executive Vice President of Guy Carpenter and had held a number of senior positions, including Head of Guy Carpenter’s U.S. Treaty Operations and Head of the firm’s Global Specialty Practices business. Mr. Zaffino has over 20 years of experience in the Insurance and Reinsurance industry. Prior to joining Guy Carpenter in 2001, he held several senior positions, most recently serving in an executive role with a GE Capital portfolio company that specialized in reinsurance.

AVAILABLE INFORMATION

The Company is subject to the informational reporting requirements of the Securities Exchange Act of 1934. In accordance with the Exchange Act, the Company files with the SEC annual reports on Form 10-K, quarterly reports on Form 10-Q and current reports on Form 8-K. The Company makes these reports and any amendments to these reports available free of charge through its website, www.mmc.com, as soon as reasonably practicable after they are filed with, or furnished to, the SEC. The public may read and copy these materials at the SEC’s Public Reference Room at 100 F Street, NE, Washington, DC, 20549. The public may obtain information on the operation of the Public Reference Room by calling the SEC at 1-800-SEC-0330. The SEC also maintains an Internet site at www.sec.gov that contains reports, proxy and information statements and other information regarding issuers, like the Company, that file electronically with the SEC.

The Company also posts on its website the following documents with respect to corporate governance:

All of the above documents are available in printed form to any Company stockholder upon request.

12

Table of Contents

Item 1A.      Risk Factors

You should consider the risks described below in conjunction with the other information presented in this report. These risks have the potential to materially adversely affect the Company’s business, results of operations or financial condition.

RISKS RELATING TO THE COMPANY GENERALLY

Legal and Regulatory Issues

We are subject to significant uninsured exposures arising from “errors and omissions” claims.

Our operating companies provide numerous professional services, including the placement of insurance and the provision of consulting, actuarial and other services for corporate and public clients around the world. As a result of these activities, the Company and its subsidiaries are subject to a significant number of errors and omissions, or “E&O,” claims, particularly in our Marsh and Mercer businesses. In our Risk and Insurance Services segment, such claims include allegations of damages arising from our failure to adequately place coverage or notify insurers of potential claims on behalf of clients. In our Consulting segment, such claims include allegations of damages arising from our consulting, actuarial and other services, which frequently involve assumptions and estimates concerning future events. Given the long-tail nature of professional liability claims, E&O matters often relate to services provided by the Company dating back many years. In each of our segments, E&O claims seek damages, including punitive and treble damages, in amounts that could, if awarded, be significant and subject us to potential liability for monetary damages, negative publicity, reputational harm and to diversion of personnel and management resources.

In establishing liabilities for errors and omissions claims in accordance with FASB ASC Subtopic No. 450-20 (Contingencies—Loss Contingencies), the Company utilizes case level reviews by inside and outside counsel and an internal actuarial analysis to estimate potential losses. A liability is established when a loss is both probable and reasonably estimable. The liability is reviewed quarterly and adjusted as developments warrant. In many cases, the Company has not recorded a liability, other than for legal fees to defend the claim, because we are unable, at the present time, to make a determination that a loss is both probable and reasonably estimable. Nevertheless, given the unpredictability of E&O claims and of litigation that could flow from them, it is possible that an adverse outcome in a particular matter could have a material adverse effect on the Company’s businesses, results of operations, financial condition or cash flow in a given quarterly or annual period.

To the extent that expected losses exceed our deductible in any policy year, the Company also records an asset for the amount that we expect to recover under any available third-party insurance programs. The Company has varying levels of third-party insurance coverage, with policy limits and coverage terms varying significantly by policy year. The Company is not aware of coverage defenses or other obstacles to coverage that would limit recoveries through policy year 2001-2002 in a material amount. Beginning in 2002, the availability of third-party insurance has declined.

Further, as more fully described in Note 16 to our consolidated financial statements included under Part II, Item 8 of this report, we are subject to legal proceedings, regulatory investigations and other contingencies other than E&O claims which, if determined unfavorably to us, could have a material adverse effect on our business, results of operations or financial condition.

Our compliance systems and controls cannot guarantee that we are in compliance with all potentially applicable U.S. federal and state or foreign laws and regulations, and actions by regulatory authorities or changes in legislation and regulation in the jurisdictions in which we operate may have an adverse effect on our business.

Our activities are subject to extensive regulation under the laws of the United States and its various states, the European Union and its member states, and the other jurisdictions in which we operate. For example, we are subject to regulation by foreign and domestic governments, regulatory agencies such as the SEC in the United States and the FSA in the United Kingdom, and self-regulatory organizations

13

Table of Contents

such as FINRA, as described further above under Part I, Item 1 — Business (Regulation) of this report. Compliance with foreign and U.S. laws and regulations that are applicable to our operations is complex and may increase our cost of doing business in international jurisdictions. These laws and regulations include import and export requirements, anti-corruption laws such as the U.S. Foreign Corrupt Practices Act and the pending anti-bribery law in the UK, local laws prohibiting corrupt payments to governmental officials, as well as various trade sanctions laws such as the various international legislative and regulatory requirements relating to trade with Iran.

As a publicly-traded company, we are subject to additional federal, state and other rules and regulations, including those required by the Sarbanes-Oxley Act of 2002 and the recently adopted Dodd-Frank Wall Street Reform and Consumer Protection Act, which will subject us to significant additional executive compensation and corporate governance requirements, many of which have yet to be implemented by the SEC. Compliance with the requirements of these laws and regulations may be costly and adversely affect our business.

While we attempt to comply with all applicable laws and regulations, there can be no assurance that we, our employees, our consultants or our contractors are in full compliance with all applicable laws and regulations or interpretations of these laws and regulations at all times or that we will be able to comply with any future laws, regulations or interpretations of these laws and regulations. If we fail to comply with applicable laws and regulations, including those referred to above, we may be subject to investigations, criminal sanctions or civil remedies, including fines, injunctions, loss of an operating license or approval, increased scrutiny or oversight by regulatory authorities, the suspension of individual employees, limitations on engaging in a particular business or redress to clients. The cost of compliance or the consequences of non-compliance could have a material adverse effect on our businesses, results of operations or financial condition. In addition, these matters could have a material adverse effect on the Company by exposing us to negative publicity, reputational damage or harm to our client or employee relationships.

In most jurisdictions, government regulatory authorities have the power to interpret or amend applicable laws and regulations, and have discretion to grant, renew and revoke various licenses and approvals we need to conduct our activities. Such authorities may require the Company to incur substantial increases in costs in order to comply with such laws and regulations. In some areas of our businesses, we act on the basis of our own or the industry’s interpretations of applicable laws or regulations, which may conflict from state to state or country to country. In the event those interpretations eventually prove different from those of regulatory authorities, we might be penalized or precluded from carrying on our previous activities. Moreover, the laws and regulations to which we are subject may conflict among the various jurisdictions and countries in which we operate. Recent changes in the regulatory environment may impact our ability to generate additional revenue streams or enhance revenue streams. Any significant impairment of our ability to conduct our business as we historically have done could have a material adverse effect on our business, results of operations or financial condition.

Finally, government involvement in the insurance or reinsurance markets could displace insurance or reinsurance currently available from the private market and adversely affect our business, results of operations or financial condition.

Improper disclosure of personal data could result in legal liability or harm our reputation.

In many jurisdictions, we may have certain obligations to maintain the security and privacy of our clients’ confidential and proprietary information and the personal information of our employees, our individual customers, and our clients’ employees and retirement and other benefit plan participants. We maintain policies, procedures and technological safeguards designed to protect the security and privacy of this information. Nonetheless, we cannot entirely eliminate the risk of improper access to or disclosure of personal information. Such disclosure could harm our reputation and subject us to liability under our contracts, as well as laws and regulations, resulting in increased costs or loss of revenue.

Further, data privacy is subject to frequently changing laws, rules and regulations in the various jurisdictions and countries in which we operate. Our failure to adhere to or successfully implement

14

Table of Contents

processes in response to changing legal or regulatory requirements in this area could result in legal liability or impairment to our reputation in the marketplace, as well as the general risks described above relating to our compliance systems and controls.

Financial Risks

Our pension obligations may cause the Company’s earnings and cash flows to fluctuate.

Volatility in equity and bond market conditions may have an unfavorable impact on the value of the Company’s pension trust assets and estimated future pension liabilities. As a result, the Company’s financial results in any period could be negatively impacted. In addition, in a period of an extended financial market downturn, the Company could be required to provide incremental pension plan funding with resulting liquidity risk which could negatively impact the Company’s financial flexibility.

The Company has significant pension obligations to its current and former employees, totaling approximately $11 billion at December 31, 2010. The magnitude of our worldwide pension plans means that our earnings and the funded status of our pension plans are comparatively sensitive to factors such as equity and bond market returns, as well as the assumed interest rates we use to discount our pension liabilities, rates of inflation and mortality assumptions. In accordance with ASC Topic No 715, the Company reflects the over- or under-funded amount of its pension plans as assets or liabilities, respectively. Variations in any of the preceding factors could cause significant fluctuation in our earnings as well as our shareholder’s equity from year to year and may result in increased levels of contributions to our pension plans.

Our results of operations could be adversely affected by economic and political conditions and the effects of these conditions on our clients’ businesses and levels of business activity.

Global economic and political conditions affect our clients’ businesses and the markets they serve. In 2008 and 2009, the credit markets and the financial services industry experienced a period of unprecedented turmoil and upheaval characterized by the bankruptcy, failure, collapse or sale of various financial institutions and an unprecedented level of intervention from the United States and foreign governments. These economic conditions have resulted in negative impacts on businesses and financial institutions, and financial services entities in particular. The global economic crisis has had a significant effect on our Consulting segment in particular. Many of our clients have been reducing expenses, including amounts they spend on consulting services. If these economic conditions persist or deteriorate, they could potentially have a significant impact on our operations.

These economic conditions may reduce demand for our services or depress pricing of those services, which could have a material adverse effect on our results of operations. Changes in global economic conditions could also shift demand to services for which we do not have competitive advantages, and this could negatively affect the amount of business that we are able to obtain. Should it become necessary for us to further restructure our business, including reducing our work force, as a result of these market conditions or other factors that reduce the demand for our products and services, our ability to execute our business strategy could be adversely affected.

Financial institution failures may cause us to incur increased expenses or make it more difficult either to utilize our existing debt capacity or otherwise obtain financing for our operations, investing activities (including the financing of any future acquisitions), or financing activities.

Our cash investments, including those held in a fiduciary capacity, are subject to general credit, liquidity, counterparty, market and interest rate risks that may be exacerbated by the recent global financial crisis. If the banking system or the fixed income, credit or equity markets deteriorate further or remain volatile, the values and liquidity of our investments could be adversely affected.

15

Table of Contents

Credit rating downgrades would increase our financing costs and could subject us to operational risk.

Both Moody’s and Standard & Poor’s downgraded the Company’s senior debt credit rating in late 2004 and S&P announced a further downgrade in December 2007. Currently, the Company’s senior debt is rated Baa2 by Moody’s and BBB- by S&P. These ratings are the next-to-lowest investment grade rating for Moody’s, and the lowest investment-grade rating for S&P.

If we need to raise capital in the future (for example, in order to fund maturing debt obligations or finance acquisitions or other initiatives), any further credit rating downgrade would increase our financing costs, and could limit our access to financing sources. Further, we believe that a downgrade to a rating below investment-grade could result in greater operational risks through increased operating costs and increased competitive pressures.

Our significant non-U.S. operations expose us to exchange rate fluctuations and various risks that could impact our business.

We are subject to exchange rate risk because some of our subsidiaries receive revenue other than in their functional currencies, and because we must translate the financial results of our foreign subsidiaries into U.S. dollars. Our U.S. operations earn revenue and incur expenses primarily in U.S. dollars. In certain jurisdictions, however, our Risk and Insurance Services operations generate revenue in a number of different currencies, but expenses are almost entirely incurred in local currency. Due to fluctuations in foreign exchange rates, we are subject to economic exposure as well as currency translation exposure on the profits of our operations. Exchange rate risk could have a significant impact on our financial condition, results of operations or cash flow.

Increased counterparty risk and changes in interest rates could reduce the value of our investment portfolio and adversely affect our financial results.

As was evident in the recent financial crisis, counterparty risk can quickly escalate resulting in substantial trading and investment losses for corporate and other investors. In addition, we may incur investment losses as a result of unusual and unpredictable market developments, and we may continue to experience reduced investment earnings if the yields on investments deemed to be low risk remain low.

We are a holding company and, therefore, may not be able to receive dividends or other distributions in needed amounts from our subsidiaries.

The Company is organized as a holding company, a legal entity separate and distinct from our operating subsidiaries. As a holding company without significant operations of our own, we are dependent upon dividends and other payments from our operating subsidiaries to meet our obligations for paying principal and interest on outstanding debt obligations, for paying dividends to stockholders and for corporate expenses. In the event our operating subsidiaries are unable to pay dividends and other payments to the Company, we may not be able to service debt, pay obligations or pay dividends on common stock.

Further, the Company derives a significant portion of its revenue and operating profit from operating subsidiaries located outside the U.S. Since the majority of financing obligations as well as dividends to stockholders are made from the U.S., it is important to be able to access cash generated outside the U.S. Funds from the Company’s operating subsidiaries outside of the U.S. are periodically repatriated to the U.S. via shareholder distributions and repayment of intercompany financing. A number of factors may arise that could limit our ability to repatriate funds or make repatriation cost prohibitive, including, but not limited to, foreign exchange rates and tax-related costs.

In the event we are unable to generate cash from our operating subsidiaries for any of the reasons discussed above, our overall liquidity could deteriorate.

16

Table of Contents

International Operations

We are exposed to multiple risks associated with the global nature of our operations.

We do business worldwide. In 2010, 56 percent of the Company’s total operating segment revenue was generated from operations outside the United States, and over one-half of our employees are located outside the United States. We expect to expand our non-U.S. operations further.

The geographic breadth of our activities subjects us to significant legal, economic, operational, market, compliance and reputational risks. These include, among others, risks relating to:

Our inability to successfully recover should we experience a disaster or other business continuity problem could cause material financial loss, loss of human capital, regulatory actions, reputational harm or legal liability.

Should we experience a local or regional disaster or other business continuity problem, such as an earthquake, hurricane, terrorist attack, pandemic, security breach, power loss, telecommunications failure or other natural or man-made disaster, our continued success will depend, in part, on the availability of our personnel, our office facilities, and the proper functioning of our computer, telecommunication and other related systems and operations. In such an event, our operational size, the multiple locations from which we operate, and our existing back-up systems would provide us with an important advantage. Nevertheless, we could still experience near-term operational challenges with regard to particular areas of our operations, such as key executive officers or personnel.

Our operations, particularly within our Consulting segment, are dependent upon our ability to protect our technology infrastructure against damage from business continuity events that could have a

17

Table of Contents

significant disruptive effect on our operations. We could potentially lose client data or experience material adverse interruptions to our operations or delivery of services to our clients in a disaster recovery scenario.

We regularly assess and take steps to improve upon our existing business continuity plans and key management succession. However, a disaster on a significant scale or affecting certain of our key operating areas within or across regions, or our inability to successfully recover should we experience a disaster or other business continuity problem, could materially interrupt our business operations and cause material financial loss, loss of human capital, regulatory actions, reputational harm, damaged client relationships or legal liability.

Competitive Risks

Each of the Company’s businesses operates in a highly competitive environment. If we fail to compete effectively, our business and results of operations will suffer.

As a global professional services firm, the Company experiences acute and continuous competition in each of its operating segments. Our ability to compete successfully depends on a variety of factors, including our geographic reach, the sophistication and quality of our services, our pricing relative to competitors and our customers’ option to self-insure or utilize internal resources instead of consultants. If we are unable to respond successfully to the competition we face, our business and results of operations will suffer.

In our Risk and Insurance Services segment, we compete intensely against a wide range of other insurance and reinsurance brokerage firms that operate on a global, regional, national or local scale for both client business and employee talent. We compete as well with insurance and reinsurance companies that market and service their insurance products without the assistance of brokers or other market intermediaries, and with various other companies that provide risk-related services. The above competition is intensified by an industry trend toward a “syndicated” or “distributed” approach to the purchase of insurance and reinsurance brokerage services, whereby a client engages multiple brokers to service different portions of the client’s account.

In our Consulting segment, we compete for business and employee talent with numerous independent consulting firms and organizations affiliated with accounting, information systems, technology and financial services firms around the world.

The loss of key professionals could hurt our ability to retain existing client revenues and generate revenues from new business.

Across all of our businesses, our personnel are crucial to developing and retaining the client relationships on which our revenues depend. It is therefore very important for us to retain significant revenue-producing employees and the key managerial and other professionals who support them. We face numerous challenges in this regard, including:

Losing employees who manage or support substantial client relationships or possess substantial experience or expertise could adversely affect our ability to secure and complete client engagements, which would adversely affect our results of operations. In addition, if any of our key professionals were to join an existing competitor or form a competing company, some of our clients could choose to use the services of that competitor instead of our services.

Consolidation in the industries that we serve could adversely affect our business.

Companies in the industries that we serve may seek to achieve economies of scale and other synergies by combining with or acquiring other companies. If two or more of our current clients merge

18

Table of Contents

or consolidate and combine their operations, it may decrease the amount of work that we perform for these clients. If one of our current clients merges or consolidates with a company that relies on another provider for its services, we may lose work from that client or lose the opportunity to gain additional work. The increased market power of larger companies could also increase pricing and competitive pressures on us. Any of these possible results of industry consolidation could adversely affect our business. Guy Carpenter is especially susceptible to this risk given the limited number of insurance company clients and reinsurers in the marketplace.

Our businesses face rapid technological changes and our failure to adequately anticipate or respond to these changes could adversely affect our business and results of operations.

To remain competitive in many of our business areas, we must identify the most current technologies and methodologies and integrate them into our service offerings. For example, Guy Carpenter’s risk-modeling services are increasingly dependent on implementing advanced software and data-compilation tools and Mercer’s ability to price its outsourcing services competitively is highly dependent on the efficient and cost effective use of technology. If we do not make the correct technology choices or investments, or if our choices or investments are insufficiently prompt or cost-effective, our business and results of operations could suffer.

Acquisitions and Dispositions

We face risks when we acquire and dispose of businesses.

We have a history of making acquisitions, including a total of 26 acquisitions in the period 2008-2010 for aggregate purchase consideration of $1.3 billion. We have also exited various businesses, including the sale of Putnam Investments Trust (“Putnam”) in August 2007 and the sale of Kroll in the third quarter of 2010. We expect that acquisitions will continue to be a key part of our business strategy. Our success in this regard will depend on our ability to identify and compete for appropriate acquisition candidates and to complete with favorable results the transactions we decide to pursue.

While we intend that our acquisitions will improve our competitiveness and profitability, we cannot be certain that our past or future acquisitions will be accretive to earnings or otherwise meet our operational or strategic expectations. Acquisitions involve special risks, including accounting, regulatory, compliance, information technology or human resources issues that could arise in connection with, or as a result of, the acquisition of the acquired company; the potential assumption of unanticipated liabilities and contingencies and difficulties in integrating acquired businesses; and acquired businesses may not achieve the levels of revenue, profit or productivity we anticipate or otherwise perform as we expect. In addition, if in the future, the performance of our reporting units or an acquired business varies from our projections or assumptions, or estimates about future profitability of our reporting units or an acquired business change, the estimated fair value of our reporting units or an acquired business could change materially and could result in an impairment of goodwill and other acquisition-related intangible assets recorded on our balance sheet or in adjustments in contingent payment amounts. Given the significant size of the Company’s goodwill and intangible assets, a write-down of this sort could have a material adverse effect on our results of operations in any given period. As of December 31, 2010, the Company’s consolidated balance sheet reflected $6.8 billion of goodwill and intangible assets, representing approximately 45 percent of the Company’s total consolidated assets and allocated by reporting segment as follows: Risk and Insurance Services, $4.7 billion and Consulting, $2.1 billion.

When we dispose of businesses we are subject to the risk, contractually agreed or otherwise, of post-transaction liabilities. For example, as described in Note 16 to our consolidated financial statements included under Part II, Item 8 of this report, we have retained certain contingent litigation liabilities relating to Putnam and Kroll.

RISKS RELATING TO OUR RISK AND INSURANCE SERVICES SEGMENT

Our Risk and Insurance Services segment, conducted through Marsh and Guy Carpenter, represented 54 percent of the Company’s total operating segment revenue in 2010. Our business in this segment is subject to particular risks.

19

Table of Contents

Results in our Risk and Insurance Services segment may be adversely affected by a general decline in economic activity.

Demand for many types of insurance and reinsurance generally rises and falls as economic growth expands or slows. This dynamic affects the level of commissions and fees generated by Marsh and Guy Carpenter. To the extent our clients become adversely affected by declining business conditions, they may choose to limit their purchases of insurance and reinsurance coverage, as applicable, which would inhibit our ability to generate commission revenue; and may decide not to purchase our risk advisory services, which would inhibit our ability to generate fee revenue. Moreover, insolvencies and combinations associated with an economic downturn, especially insolvencies and combinations in the insurance industry, could adversely affect our brokerage business through the loss of clients or by hampering our ability to place insurance and reinsurance business. Guy Carpenter is especially susceptible to this risk given the limited number of insurance company clients and reinsurers in the market place.

Volatility or declines in premiums and other market trends may significantly impede our ability to improve revenues and profitability.

A significant portion of our Risk and Insurance Services revenue consists of commissions paid to us out of the premiums that insurers and reinsurers charge our clients for coverage. Our revenues and profitability are subject to change to the extent that premium rates fluctuate or trend in a particular direction. The potential for changes in premium rates is significant, due to the general phenomenon of pricing cyclicality in the commercial insurance and reinsurance markets.

In addition to movements in premium rates, our ability to generate premium-based commission revenue may be challenged by the growing availability of alternative methods for clients to meet their risk-protection needs. This trend includes a greater willingness on the part of corporations to “self-insure;” the use of so-called “captive” insurers; and the advent of capital markets-based solutions to traditional insurance and reinsurance needs. Further, the profitability of our Risk and Insurances Services segment depends in part on ensuring that our professionals are compensated not only for insurance and reinsurance transactions, but for the increasing analytical services and advice that we provide. If we are unable to achieve and maintain adequate billing rates for all of our services, our margins and profitability could suffer.

RISKS RELATING TO OUR CONSULTING SEGMENT

Our Consulting segment, conducted through Mercer and Oliver Wyman Group, represented 46 percent of our total operating segment revenue in 2010. Our businesses in this segment is subject to particular risks.

Demand for our services might decrease for various reasons, including a general economic downturn, a decline in a client’s or an industry’s financial condition, or changes in government regulation.

Our Consulting segment has historically achieved significant annual revenue growth. Despite this history, however, the recent global economic conditions have resulted in negative impacts on businesses and financial institutions. Many of our clients, including financial institutions, corporations, governmental entities and pension plans, have been reducing expenses, including amounts spent on consulting services. The evolving needs or financial circumstances of our clients may challenge our ability to increase revenues and profitability and reduce demand for our services. If the economy or markets in which we operate experience continued weakness at current levels or deteriorate further, our business, financial condition and results of operations could be materially and adversely affected.

In addition, demand for many of Mercer’s benefits services is affected by government regulation and tax rules, which drive our clients’ needs for benefits-related services. For example, significant changes in government regulations affecting the value, use or delivery of benefits and human resources programs, including changes in regulations relating to health and welfare plans, defined contribution plans, or defined benefit plans, may adversely affect the demand for or profitability of Mercer’s services.

20

Table of Contents

Factors impacting defined benefit pension plans could adversely affect Mercer.

Mercer currently provides corporate, multi-employer and public clients with consulting and actuarial services relating to defined benefit pension plans. The nature of our work, particularly our actuarial services, is complex, and involves numerous assumptions and estimates regarding future events, including interest rates used to discount future liabilities, estimated rates of return for a plan’s assets, healthcare cost trends or participants’ life expectancies. Clients dissatisfied with our services have brought, and may bring, claims against us. In addition, over the past several years, the funded status of defined benefit pension plans has declined markedly. A number of Mercer’s clients have frozen or curtailed their defined benefit plans and moved to defined contribution plans resulting in reduced revenue for Mercer’s retirement business. These developments could adversely affect Mercer’s business and operating results.

Our profitability may suffer if we are unable to achieve or maintain adequate utilization and pricing rates for our consultants.

The profitability of our Consulting businesses depends in part on ensuring that our consultants maintain adequate utilization rates (i.e., the percentage of our consultants’ working hours devoted to billable activities). Our utilization rates are affected by a number of factors, including:

The factors listed above, and therefore also our utilization rates for service personnel, have been adversely affected by recent macroeconomic conditions. If the utilization rate for our consulting professionals continues to decline, our profit margin and profitability would suffer.

In addition, the profitability of our Consulting businesses depends on the prices we are able to charge for our services. Our pricing power is affected by a number of factors, including:

Our pricing has also been adversely affected by the recent economic crisis. If we are unable to achieve and maintain adequate billing rates for our services, our margins and profitability could suffer.

21

Table of Contents

Our quarterly revenues and profitability may fluctuate significantly.

Quarterly variations in revenues and operating results at Mercer and Oliver Wyman Group may occur due to several factors. These include:

A significant portion of total operating expenses at Mercer and Oliver Wyman Group is relatively fixed. Therefore, a variation in the number of client assignments or in the timing of the initiation or the completion of client assignments can cause significant variations in quarterly operating results for these businesses.

If we are unable to collect our receivables or unbilled services, our results of operations and cash flows could be adversely affected.

Our business depends on our ability to successfully obtain payment from our clients of the amounts they owe us for work performed. We evaluate the financial condition of our clients and usually bill and collect on relatively short cycles. There is no guarantee that we will accurately assess the creditworthiness of our clients. Macroeconomic conditions could also result in financial difficulties for our clients, and as a result could cause clients to delay payments to us, request modifications to their payment arrangements that could increase our receivables balance, or default on their payment obligations to us. The increasing number of insolvencies in the current economic environment and the numerous bankruptcy laws to which they are subject could also adversely affect our ability to collect receivables or unbilled services. Timely collection of client balances depends on our ability to complete our contractual commitments and bill and collect our contracted revenues. If we are unable to meet our contractual requirements, we might experience delays in collection of and/or be unable to collect our client balances, and if this occurs, our results of operations and cash flows could be adversely affected. In addition, if we experience an increase in the time to bill and collect for our services, our cash flows could be adversely affected.

Item 1B.      Unresolved Staff Comments.

There are no unresolved comments to be reported pursuant to Item 1B.

22

Table of Contents

Item 2.      Properties.

Marsh & McLennan Companies and its subsidiaries maintain their corporate headquarters in and around New York City. We also maintain other offices around the world, primarily in leased space. In certain circumstances we may have space that we sublet to third parties, depending upon our needs in particular locations.

Marsh & McLennan Companies and certain of its subsidiaries own, directly and indirectly through special-purpose subsidiaries, a 55% condominium interest covering approximately 900,000 square feet in a 44-story building in New York City. This real estate serves as the Company’s New York headquarters and is occupied primarily by the Company and its affiliates for general corporate use. The remaining 45% condominium interest in the 1166 Property is owned by an unaffiliated third party. The Company’s owned interest is financed by a 30-year loan that is non-recourse to the Company (except in the event of certain prohibited actions) and secured by a first mortgage lien on the condominium interest and a first priority assignment of leases and rents. In the event (1) the Company is downgraded below B/B2 (Stable) by any of S&P, Fitch and Moody’s or (2) an event of default has occurred and is continuing, the Company would be obligated to pre-fund certain reserve accounts relating to the mortgaged property, including a rent reserve account in an amount equal to three months rent for the entire occupancy of the mortgaged property.

Item 3.      Legal Proceedings.

Information regarding legal proceedings is set forth in Note 16 to the consolidated financial statements appearing under Part II, Item 8 (“Financial Statements and Supplementary Data”) of this report.

23

Table of Contents

PART II

Item 5.      Market for the Company’s Common Equity, Related Stockholder Matters and Issuer Purchases of Equity Securities.

For information regarding dividends paid and the number of holders of the Company’s common stock, see the table entitled “Selected Quarterly Financial Data and Supplemental Information (Unaudited)” below on the last page of Part II, Item 8 (“Financial Statements and Other Supplementary Data”) of this report.

The Company’s common stock is listed on the New York, Chicago and London Stock Exchanges. The following table indicates the high and low prices (NYSE composite quotations) of the Company’s common stock during 2010 and 2009 and each quarterly period thereof:

On February 18, 2011, the closing price of the Company’s common stock on the NYSE was $30.78.

Pursuant to a September 2010 authorization by the Company’s Board of Directors to repurchase shares of its common stock up to a dollar value of $500 million, the Company repurchased 3,365,889 shares of its common stock during the fourth quarter of 2010. The Company remains authorized to repurchase shares of its common stock up to a dollar value of approximately $414.5 million. There is no time limit on this authorization.

24

Table of Contents

Item 6.      Selected Financial Data.

Marsh & McLennan Companies, Inc. and Subsidiaries

FIVE-YEAR STATISTICAL SUMMARY OF OPERATIONS

See Management’s Discussion and Analysis of Financial Condition and Results of Operations, appearing under Amended Item 7 of this report, for discussion of significant items affecting our results of operations in 2010, 2009 and 2008.

25

Table of Contents

Item 7. Management’s Discussion and Analysis of Financial Condition and Results of Operations.

General

Marsh & McLennan Companies, Inc. and Subsidiaries (the “Company”) is a global professional services firm providing advice and solutions in the areas of risk, strategy, and human capital. The Company’s subsidiaries include Marsh, which provides risk and insurance services; Guy Carpenter, which provides reinsurance services; Mercer, which provides human resource and related financial advice and services; and Oliver Wyman Group, which provides management consulting and other services. The Company’s approximately 51,000 employees worldwide provide analysis, advice and transactional capabilities to clients in over 100 countries.

The Company’s business segments are based on the services provided. Risk and Insurance Services includes risk management and insurance and reinsurance broking and services, provided primarily by Marsh and Guy Carpenter. Consulting, which comprises the activities of Mercer and Oliver Wyman Group, includes human resource consulting and related investment and outsourcing services, and specialized management, economic and brand consulting services.

In the first quarter of 2010, Kroll completed the sale of Kroll Laboratory Specialists (KLS) and on August 3, 2010, the Company completed the sale of Kroll to Altegrity for cash consideration of $1.13 billion. The account balances and activities of Kroll and KLS were segregated and reported as discontinued operations in the accompanying consolidated balance sheets and the accompanying consolidated statements of income. During the second quarter of 2009, Kroll sold Kroll Government Services (“KGS”), which has been classified as a discontinued operation. In 2008, the Company disposed of its U.S. and U.K. restructuring businesses to their respective management teams in separate leveraged buyouts.

With the Kroll disposition completed in August 2010, along with the previous disposals of other businesses between 2008 and 2010, the Company has now divested its entire Risk Consulting and Technology segment. As described in Note 1 to the consolidated financial statements, based on the terms and conditions of the divestitures of the Corporate Advisory and Restructuring businesses (“CARG”) in 2008, the Company determined it has “continuing involvement” in those businesses, as that term is used in SEC Staff Accounting Bulletin Topic 5e. Therefore classification of CARG as discontinued operations is not appropriate, and their financial results in the current and prior periods are included in operating income. The runoff of the Company’s involvement in the CARG businesses is now managed by the Company’s corporate departments, and consequently, the financial results of these businesses are now included in “Corporate” for segment reporting purposes.

We describe the primary sources of revenue and categories of expense for each segment below, in our discussion of segment financial results. A reconciliation of segment operating income to total operating income is included in Note 17 to the consolidated financial statements included in Part II Item 8 in this report. The accounting policies used for each segment are the same as those used for the consolidated financial statements.

This MD&A contains forward-looking statements as that term is defined in the Private Securities Litigation Reform Act of 1995. See “Information Concerning Forward-Looking Statements” at the outset of this report.

Significant Developments

The Company’s historical financial information should be viewed in light of the significant developments discussed below.

26

Table of Contents

27

Table of Contents

Consolidated Results of Operations

Consolidated operating income was $939 million in 2010 compared with $778 million in the prior year. The 2010 results include a $400 million charge, net of insurance recoveries, for the resolution of the litigation brought by the ARMB and restructuring and other noteworthy charges of $139 million. The 2009 results include a $230 million charge, net of insurance recoveries, for the settlement of the securities and ERISA class action lawsuits filed in 2004 and restructuring and other noteworthy items of $264 million. Excluding these charges, consolidated operating income was $1.5 billion in 2010 compared with $1.3 billion in 2009.

Risk and Insurance Services operating income increased $176 million to $972 million in 2010 compared with 2009, or 22%, resulting from revenue growth at both Marsh and Guy Carpenter, as well as a decrease of $77 million in restructuring and related charges.

Consulting operating income decreased $276 million to $129 million in 2010 primarily due to the $400 million net charge related to the ARMB litigation settlements, partly offset by lower restructuring and other noteworthy items of $48 million. Excluding these items, Consulting operating income increased $76 million, or 16%.

Corporate and other results were $162 million of expense in 2010 compared to net expense of $423 million in 2009. In 2010, Corporate and other expenses include restructuring and other noteworthy charges of $13 million, partly offset by $10 million of payments received by the Company related to CARG. In 2009, Corporate expenses include a net charge of $230 million related to settlements of the class action lawsuits described above and $33 million of restructuring and other noteworthy charges. Excluding these items, Corporate and other expenses decreased $1 million in 2010 compared with 2009.

Discontinued operations include the operating results of Kroll for all years presented, including goodwill impairment charges of $315 million and $504 million in 2009 and 2008, respectively, the gain on the sale of Kroll and KLS in 2010 of $282 million, insurance recoveries of $16 million related to Putnam market-timing related matters in 2010 and the loss on the sale of KGS in 2009. Discontinued operations also include the accretion of interest related to an indemnity for uncertain tax positions provided as part of the purchase by Great-West Life Co. Inc., of Putnam Investments Trust from the Company in August 2007.

28

Table of Contents

Consolidated net income attributable to the Company was $855 million in 2010, compared with $227 million in 2009.

Consolidated Revenues and Expenses

The Company conducts business in many countries, as a result of which the impact of foreign exchange rate movements may impact period-to-period comparisons of revenue. Similarly, the revenue impact of acquisitions and dispositions may impact period-to-period comparisons of revenue. Underlying revenue measures the change in revenue from one period to another by isolating these impacts. The impact of foreign currency exchange fluctuations, acquisitions and dispositions on the Company’s operating revenues is as follows:

Revenue Details

The following table provides more detailed revenue information for certain of the components presented above:

29

Table of Contents