EY (formerly Ernst & Young) is a multinational professional services firm headquartered in London, England. EY is one of the largest professional services firms in the world and is one of the "Big Four" accounting firms. The organisation operates as a network of member firms which are separate legal entities in individual countries. It has 231,000 employees in over 700 offices around 150 countries in the world. It provides assurance (including financial audit), tax, consulting and advisory services to companies.