Marsh & McLennan Companies is a global professional services firm founded in 1871 with four main businesses: Marsh, Guy Carpenter, Mercer, and Oliver Wyman. It has over 60,000 employees worldwide providing risk management, insurance broking, reinsurance, management consulting, and human resources consulting. The document outlines MMC's history and growth over 145 years through acquisitions and expanding globally to serve clients in over 130 countries. It emphasizes the company's purpose of helping address challenges through expertise in risk, strategy, and people.