This summary highlights information contained elsewhere in this proxy statement. You should read the entire proxy statement carefully before voting.

We describe key features of the Company’s corporate governance environment below and in the next section of this proxy statement, captioned “Board of Directors and Committees.” Our key corporate governance materials are available online at http://www.mmc.com/about/governance.php.

Overview

Our Board of Directors currently has twelve (12) members, including H. Edward Hanway, our independent chairman, and Daniel S. Glaser, our President and Chief Executive Officer. Mr. Glaser is the only member of management who serves as a director. As described in more detail under “Board of Directors and Committees,” our Board maintains an Audit Committee, a Compensation Committee, a Directors and Governance Committee, a Finance Committee, a Corporate Responsibility Committee and an Executive Committee.

Corporate Governance Practices

The Company is committed to best practices in corporate governance. Highlights of our corporate governance practices are described below.

BOARD STRUCTURE

ELECTION OF DIRECTORS

PROXY ACCESS

RIGHT OF STOCKHOLDERS TO CALL SPECIAL MEETINGS

STOCKHOLDER RIGHTS PLAN

COMPENSATION PRACTICES

EQUITY OWNERSHIP AND HOLDING REQUIREMENTS

Guidelines for Corporate Governance

The Company and the Board of Directors formally express many of our governance policies through our Guidelines for Corporate Governance (our “Governance Guidelines”). The Governance Guidelines are posted on our website at http://www.mmc.com/about/governance.php.

The Governance Guidelines summarize certain policies and practices designed to assist the Board in fulfilling its fiduciary obligations to the Company’s stockholders, including the following (parenthetical references are to the relevant section of the Governance Guidelines):

Director Independence

The Board has determined that all directors other than Mr. Glaser are independent under the New York Stock Exchange (“NYSE”) listed company rules and the standards set forth in the Governance Guidelines. Therefore, the Board has satisfied the objective, set forth in the Governance Guidelines, that a substantial majority of the Company’s directors be independent of management.

For a director to be considered independent, the Board must affirmatively determine that the director has no direct or indirect material relationship with the Company. The Board has established standards to assist it in making determinations of director independence. These standards conform to, or are more exacting than, the independence requirements provided in the NYSE listed company rules. The Company’s director independence standards are set forth as Annex A to our Governance Guidelines.

All members of the Audit, Compensation and Directors and Governance Committees must be independent directors under the NYSE listed company rules and the standards set forth in the Company’s Governance Guidelines. Members of the Audit Committee must also satisfy a separate Securities and Exchange Commission (“SEC”) and NYSE independence requirement, which provides that they may not be affiliates and may not accept directly or indirectly any consulting, advisory or other compensatory fee from the Company or any of its subsidiaries, other than their directors’ compensation. The Board evaluated each member of the Compensation Committee under the additional NYSE compensation committee member independence standards and also determined that these members qualify as “non-employee directors” (as defined under Rule 16b-3 under the Securities Exchange Act of 1934) and as “outside directors” (as defined in Section 162(m) of the Internal Revenue Code).

Under our Governance Guidelines, if a director whom the Board has deemed independent has a change in circumstances or relationships that might cause the Board to reconsider that determination, he or she must immediately notify the chairman of the Board and the chair of the Directors and Governance Committee.

Board and Committee Evaluations

The Directors and Governance Committee oversees an annual evaluation of the Board’s performance and effectiveness. The evaluation focuses on the Board’s contribution to the Company over the preceding year, including areas in which the Board or management believes the Board could enhance its future contributions. As part of the Board’s self-evaluation process, each director completes a questionnaire soliciting quantitative ratings and qualitative commentary. The questionnaire solicits feedback on topics such as the Board’s key priorities and fulfillment of the Board’s responsibilities under our Governance Guidelines. The responses to the questionnaire are compiled on an unattributed basis and are discussed by the Board in executive session. Based on the evaluation results, changes in practices or procedures are considered and, as appropriate, implemented. More generally, directors are encouraged to make suggestions at any time for improving the Board’s practices.

In addition, each of the Audit, Compensation and Directors and Governance Committees evaluates its own performance annually pursuant to their respective charters. Each Committee’s self-evaluation is conducted in an executive session and includes an assessment of its fulfillment of its responsibilities under its charter and our Governance Guidelines.

Codes of Conduct

Our reputation is fundamental to our business. The Company’s directors and officers and other employees are expected to act ethically at all times. To provide guidance in this regard, the Company has adopted a Code of Conduct, The Greater Good, which applies to all of our directors, officers and other employees. The Greater Good has been distributed to the Company’s employees, accompanied by a comprehensive training and communication effort that included a campaign in 2016 requiring employees to recertify their commitment to The Greater Good. The Company has also adopted an additional Code of Ethics for the Chief Executive Officer and Senior Financial Officers, which applies to our chief executive officer, chief financial officer and controller. Both of these codes are posted on the Company’s website at http://www.mmc.com and print copies are available to any stockholder upon request. We will disclose any amendments to, or waivers of, the Code of Ethics for the Chief Executive Officer and Senior Financial Officers on our website within four business days.

Review of Related Person Transactions

The Company maintains a written Policy Regarding Related Person Transactions, which sets forth standards and procedures for the review and approval or ratification of transactions between the Company and related persons. The policy is administered by the Directors and Governance Committee with assistance from the Company’s Corporate Secretary.

In determining whether to approve or ratify a related person transaction, the Directors and Governance Committee will review the facts and circumstances including: the commercial reasonableness of the transaction; the benefits of the transaction to the Company; the availability of other sources for the products or services involved in the transaction; the materiality and nature of the related person’s direct or indirect interest in the transaction; the potential public perception of the transaction and the potential impact of the transaction on the independence of any of the Company’s directors. The Directors and Governance Committee will approve or ratify a related person transaction only if the Committee determines that the related person transaction is in, or is not inconsistent with, the best interests of the Company and its stockholders.

If the Directors and Governance Committee determines not to approve or ratify a related person transaction, the transaction will not be entered into or continued. No member of the Directors and Governance Committee will participate in any review or determination if the Committee member or any of his or her immediate family members is the related person.

See the discussion under “Transactions with Management and Others” on page 65.

Communicating Concerns Regarding Accounting Matters

The Audit Committee of the Board of Directors has established procedures to enable anyone who has a concern about the Company’s accounting, internal accounting controls or auditing practices to communicate that concern directly to the Audit Committee. These communications, which may be made on a confidential or anonymous basis, may be submitted in writing, by telephone or online as follows:

By mail to:

Marsh & McLennan Companies, Inc.

Audit Committee of the Board of Directors

c/o Katherine J. Brennan—Corporate Secretary

1166 Avenue of the Americas, Legal Department

New York, New York 10036-2774

By telephone or online:

Go to this website for dialing instructions or to raise a concern online:

http://www.ethicscomplianceline.com

Further details of the Company’s procedures for handling complaints and concerns of employees and other interested parties regarding accounting matters are posted on our website at http://www.mmc.com/about/governance.php.

Company policy prohibits retaliation against anyone who raises a concern in good faith.

Communicating with Directors

Holders of the Company’s common stock and other interested parties may send communications to the Board of Directors, the independent chairman, any of the directors or the independent directors as a group by mail (addressed to Katherine J. Brennan—Corporate Secretary at the address shown above), online at http://www.ethicscomplianceline.com or by telephone (local dialing instructions can be found at http://www.ethicscomplianceline.com). Items unrelated to the directors’ duties and responsibilities as Board members may be excluded by the Corporate Secretary, including solicitations and advertisements, junk mail, product-related communications, surveys and job referral materials such as resumes.

Board Composition, Leadership and Size

At the 2018 annual meeting, stockholders will vote on the election of twelve (12) directors. H. Edward Hanway currently serves as the Board’s independent chairman.

The only member of management who serves on the Board is Daniel S. Glaser, the Company’s President and Chief Executive Officer. The position of chairman of the Board has been held by an independent director since 2005. The Board believes that this currently is the best leadership structure for the Company.

Director Qualifications and Nomination Process

The Board, taking into account the recommendation of the Directors and Governance Committee, is responsible for nominating a slate of director candidates for election at the Company’s annual meeting of stockholders. The Board has delegated to the Directors and Governance Committee the authority to identify, screen and recommend to the Board potential new director candidates and to engage one or more search firms to assist the Committee in that regard. The Directors and Governance Committee periodically reviews with the Board the skills and characteristics to be sought in any new director candidates, as well as the overall composition and structure of the incumbent Board, taking into account such factors as the Board’s current mix and diversity of skills, backgrounds and experiences.

As provided in our Governance Guidelines, all directors must demonstrate the highest standards of ethics and integrity, must be independent thinkers with strong analytical ability and must be committed to representing all of the Company’s stockholders rather than any particular interest group.

In addition to these characteristics, our Governance Guidelines provide that each director candidate be evaluated by the Board against the following criteria: (1) the candidate’s personal and professional reputation and background; (2) the candidate’s industry knowledge; (3) the candidate’s experience with businesses or other organizations comparable to the Company in terms of size or complexity; (4) the interplay of the candidate’s skills and experience with those of the incumbent directors; (5) the extent to which the candidate would provide substantive expertise that is currently sought by the Board or any committees of the Board; (6) the candidate’s ability to commit the time necessary to fulfill a director’s responsibilities; (7) relevant legal and regulatory requirements and evolving best practices in corporate governance; (8) the gender, racial, ethnic and cultural diversity of each potential candidate and (9) any other criteria the Board deems appropriate.

Director Skills and Experience

The chart below identifies the five principal skills that the Directors and Governance Committee considered for each director when evaluating that director’s experience and qualifications to serve as a director. In addition, the chart provides descriptions for each area of expertise. Additional information about each director’s background, business experience and other matters, as well a description of how each individual’s experience qualifies him or her to serve as a director of the Company is provided under the heading “Item 1—Election of Directors” beginning on page 13.

Board Diversity

We are committed to maintaining a diverse and inclusive Board. Of our twelve directors, five (42%) are diverse, including two women.

Our Governance Guidelines specify that the gender, racial, ethnic and cultural diversity of each potential director candidate be considered by the Board. In its recruitment process, the Directors and Governance Committee and the Board seek to reflect gender, racial, ethnic and cultural diversity in the pool of director candidates.

Stockholder Nominations for Director Candidates

The Directors and Governance Committee will consider director candidates recommended by stockholders if the recommendation is submitted in writing at the address below. As described in Article III of the Company’s bylaws, stockholders may submit nominations of persons for election as directors of the Company at an annual meeting of stockholders provided that the proposing stockholder is a stockholder of record both at the time the nomination is submitted and at the time of the annual meeting, is entitled to vote at the annual meeting and complies with the notice procedures set forth in Sections 3.01 and 3.02 of the bylaws. The notice of nomination must meet bylaw requirements as to timeliness and form and be delivered to the Company’s Corporate Secretary at our principal executive offices: Marsh & McLennan Companies, Inc., Attn: Directors and Governance Committee, c/o Katherine J. Brennan—Corporate Secretary, 1166 Avenue of the Americas, New York, New York 10036-2774. See the discussion under “Submission of Stockholder Proposals and Other Items of Business for 2019 Annual Meeting” on page 70.

Director Election Voting Standard

The Company’s bylaws provide that, in an uncontested election of directors (i.e., where the number of nominees does not exceed the number of directors to be elected), a director nominee must receive more votes cast “for” than “against” his or her election in order to be elected to the Board.

In connection with the Company’s majority voting standard for director elections, the Board has adopted the following procedures, which are set forth more fully in Section E.3 of our Governance Guidelines:

Attendance

The Board held eight meetings, including telephonic meetings, during 2017. All directors attended at least 75% of the meetings of the Board and committees on which they served. The Board’s policy is to have all directors attend annual meetings of stockholders. All of our directors were present at the 2017 annual meeting of stockholders.

Board Refreshment

The Board is committed to effective succession planning and refreshment. Two directors have joined since 2016, enhancing the Board’s breadth and depth of experience and diversity. The average tenure of our directors is eight years. As part of the process for nominating director candidates, the Board evaluates each individual director in the context of the Board as a whole, with the objective of recommending a group that can best support the success of our business and represent stockholder interests.

Retirement

Our Governance Guidelines require our independent directors to resign no later than at the annual meeting of stockholders following their 75th birthday. Any director who is an employee of the Company will resign from the Board when his or her employment ends.

Executive Sessions

Our independent directors meet in executive session without management at regularly scheduled in-person Board meetings. In 2017 they held eight executive sessions, which were presided over by the independent chairman of the Board. In addition, the members of the Audit, Compensation and Directors and Governance Committees meet in executive session without management at regularly scheduled in-person committee meetings.

Risk Oversight

It is the responsibility of the Company’s senior management to assess and manage our exposure to risk and to bring to the Board of Directors’ attention the most material risks facing the Company. The Board oversees risk management directly and through its committees. Annually, the Board reviews management’s assessment of the Company’s key enterprise risks. The Audit Committee regularly reviews the Company’s policies and practices with respect to risk assessment and risk management. The Directors and Governance Committee considers risks related to CEO succession planning and the Compensation Committee considers risks relating to the design of executive compensation programs and arrangements. See below for additional information about the Board’s committees.

Committees

Our Board maintains an Audit Committee, a Compensation Committee, a Directors and Governance Committee, a Finance Committee, a Corporate Responsibility Committee and an Executive Committee to assist the Board in discharging its responsibilities. Following each committee meeting, the respective committee chair reports the highlights of the meeting to the full Board.

Membership on each of the Audit, Compensation and Directors and Governance Committees is limited to independent directors as required by the Company, the listing standards of the NYSE and the SEC’s independence rules. The charters for these committees can be viewed on our website at http://www.mmc.com/about/governance.php.

The table below indicates committee assignments for 2017 and the number of times each committee met in 2017:

AUDIT COMMITTEE

The Audit Committee is charged, among other things, with assisting the Board in fulfilling its oversight responsibilities with respect to:

The Audit Committee selects, oversees and approves, pursuant to a pre-approval policy, all services to be performed by our independent registered public accounting firm. The Company’s independent registered public accounting firm reports to the Audit Committee.

All members of the Audit Committee are “financially literate,” as required by the NYSE and determined by the Board. The Board has determined that Anthony K. Anderson, Bruce P. Nolop, Marc D. Oken and Lloyd M. Yates have the requisite qualifications to satisfy the SEC definition of “audit committee financial expert.”

COMPENSATION COMMITTEE

The primary responsibilities of the Compensation Committee are to:

Meeting Schedule.  The Compensation Committee met seven times in 2017, including a special meeting in February to complete its annual review of, and make decisions on, executive compensation. Decisions relating to significant matters are usually presented to the Compensation Committee and discussed at more than one meeting to allow for full consideration of the implications and possible alternatives before a final decision is made. The Compensation Committee receives support from its independent compensation consultant and the Company’s management, including the Company’s human resources staff, as described below. At each of its meetings, the Compensation Committee meets in executive session and without management present. The independent compensation consultant attends portions of the executive sessions.

The Compensation Committee may delegate all or a portion of its duties and responsibilities to the chair of the Compensation Committee or a subcommittee of the Compensation Committee. If necessary, the chair is authorized to take action on behalf of the Compensation Committee between its regularly scheduled meetings, within prescribed guidelines. If any such action is taken, the chair reports such action to the Compensation Committee at its next regularly scheduled meeting.

Independent Compensation Consultant.  The Compensation Committee has engaged Pay Governance LLC as its independent compensation consultant to support the Compensation Committee in performing its duties and to make recommendations to the Compensation Committee regarding our executive compensation program. The independent compensation consultant reports directly to the Compensation Committee and provides advice and analysis solely to the Compensation Committee. The independent compensation consultant supports the Compensation Committee by:

The Compensation Committee requested and received advice from the independent compensation consultant with respect to all significant matters addressed by the Compensation Committee during 2017. Except for the services provided to the Board, neither the individual compensation consultant nor Pay Governance LLC nor any of its affiliates provided any services to the Company or its affiliates in 2017.

The Compensation Committee assessed the work of Pay Governance LLC during 2017 pursuant to SEC rules and concluded that Pay Governance’s work did not raise any conflict of interest.

Company Management.  The Company’s management, including the Company’s human resources staff, supports the Compensation Committee by:

In addition, our President and Chief Executive Officer provides recommendations with respect to the compensation of our other senior executives.

Our President and Chief Executive Officer, senior members of the Company’s human resources staff and internal legal counsel attended Compensation Committee meetings when invited but were not present for executive sessions or for any discussion of their own compensation.

Timing and Procedures of Equity-Based Compensation Awards.  Annual awards under our LTI compensation program are approved at a prescheduled meeting of the Compensation Committee each February and, consistent with our historical practice, are granted on that same date.

In addition, the Compensation Committee periodically grants restricted stock unit awards to newly hired senior executives and to continuing senior executives for increased responsibilities that accompany changes in position and for retention purposes. These awards are approved at prescheduled meetings of the Compensation Committee. The Compensation Committee has also authorized our President and Chief Executive Officer to make such awards to individuals who are not senior executives, subject to prescribed parameters. These awards are granted on the first calendar day of the month following approval of the award by the Compensation Committee or our President and Chief Executive Officer, as applicable. In the event that an award is approved prior to an individual’s start date with the Company, the award will be granted on the first calendar day of the first month on or following the individual’s start date; however, if an award is approved contingent on the award recipient providing documentation supporting the forfeiture of compensation from a former employer and that documentation has not been provided as of the individual’s start date, the award will be granted on the first calendar day of the month following the provision of such documentation and acceptance by the Company.

Typically, equity-based awards are denominated as a dollar value and then converted into a number of performance stock units, restricted stock units or stock options. The number of performance stock units or restricted stock units is determined based on the grant date fair value of the Company’s common stock, which is defined as the average of the high and low trading prices of the Company’s common stock on the trading day immediately preceding the grant date. The number of stock options is determined based on the grant date fair value of a stock option to purchase a share of the Company’s common stock. The grant date fair value of stock options is determined in accordance with Financial Accounting Standards Board Accounting Standards Codification Topic 718, Compensation-Stock Compensation (“FASB ASC Topic 718”). Stock options have an exercise price equal to the average of the high and low trading prices of the Company’s common stock on the trading day immediately preceding the grant date. We believe that our equity-based compensation grant procedures effectively protect against the manipulation of grant timing for employee gain.

The Company’s human resources staff regularly monitors, and updates the Compensation Committee on, the use of shares of the Company’s common stock for equity-based awards and the number of shares available for future awards under our equity-based compensation plans. As part of the process of granting annual LTI compensation, the Compensation Committee considers share use and equity run rate (as defined in “2017 Highlights” on page 22) so that annual LTI awards, and the extent to which shares of the Company’s common stock are used for those awards, are maintained at a reasonable level.

DIRECTORS AND GOVERNANCE COMMITTEE

The Directors and Governance Committee’s duties and responsibilities include, among other things:

FINANCE COMMITTEE

The Finance Committee reviews and makes recommendations to the Board concerning, among other matters, the Company’s capital structure, capital management and methods of corporate finance (including proposed issuances of securities or other financing transactions) and proposed acquisitions, divestitures or other strategic transactions.

CORPORATE RESPONSIBILITY COMMITTEE

The Corporate Responsibility Committee’s purpose is to create value for our stakeholders by enhancing the Company’s reputation, business position and employee engagement. In particular, the Corporate Responsibility Committee focuses on government relations, corporate communications, social responsibility, diversity and inclusion and sustainability and reports to the Board on a regular basis.

EXECUTIVE COMMITTEE

The Executive Committee is empowered to act for the full Board during the intervals between Board meetings, except with respect to matters that, under Delaware law or the Company’s bylaws, may not be delegated to a committee of the Board. The Executive Committee meets as necessary, with all actions taken by the Committee reported at the next Board meeting.

Director Compensation

EXECUTIVE DIRECTORS

Executive directors (currently only Mr. Glaser) receive no compensation for their service as directors.

INDEPENDENT DIRECTORS

Independent directors receive a basic annual retainer and annual stock grant as compensation for their service as directors. Our independent chairman and directors who serve as the chair of a committee also receive a supplemental annual retainer. The basic annual retainer and the supplemental retainers are paid quarterly for pay periods ending on August 15, November 15, February 15 and May 15. Under the terms of the Company’s Directors’ Stock Compensation Plan, independent directors may elect to receive these retainer amounts in cash, the Company’s common stock or a combination thereof and may defer receipt of all or a portion of any compensation to be paid in the form of the Company’s common stock until a specified future date. The annual stock grant is made on June 1st of each year. Independent directors are also eligible to participate in the Company’s matching-gift program for certain charitable gifts to educational institutions.

The Board’s compensation year runs from June 1 through May 31. The current compensation arrangements for independent directors are summarized in the table below.

Elements of Independent Director Compensation

2017 Independent Director Compensation

The table below indicates total compensation received by our independent directors for service on the Board and its committees during 2017:

Item 1 — Election of Directors

At the 2018 annual meeting, stockholders will vote on the election of the twelve (12) nominees listed below for a one-year term—Anthony K. Anderson, Oscar Fanjul, Daniel S. Glaser, H. Edward Hanway, Deborah C. Hopkins, Elaine La Roche, Steven A. Mills, Bruce P. Nolop, Marc D. Oken, Morton O. Schapiro, Lloyd M. Yates and R. David Yost.

The Board has nominated each of these individuals to serve until the 2019 annual meeting. Each nominee has indicated that he or she will serve if elected. We do not anticipate that any of the nominees will be unable or unwilling to stand for election, but if that happens, your proxy may be voted for another person nominated by the Board or the Board may reduce its size. Each director holds office until his or her successor has been duly elected and qualified or his or her earlier resignation, death or removal.

In nominating the following slate of director candidates for election at the Company’s annual meeting of stockholders, the Board has evaluated each nominee by reference to the criteria described above on pages 5 and 6 under the headings “Director Qualifications and Nomination Process” and “Director Skills and Experience.” In addition, the Board evaluates each individual director in the context of the Board as a whole, with the objective of recommending a group that can best support the success of our businesses and represent stockholder interests.

The following section contains information provided by the nominees about their principal occupations, business experience and other matters, including their 2018 committee assignments, as well as a description of how each individual’s experience qualifies him or her to serve as a director of the Company.

The Board of Directors recommends that you vote FOR all of the director nominees.