EY (formerly Ernst & Young) is a multinational professional services firm headquartered in London, United Kingdom. In 2016 it was the third largest of the "Big Four" professional services firms, behind Deloitte and PwC. The organization 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.