Ernst & Young (branded as EY) is a multinational professional services firm headquartered in London. It was the third largest professional services firm in the world by aggregated revenue in 2012 and is one of the "Big Four" accounting firms. The organization operates as a network of member firms which are separate legal entities in individual countries. It has 167,000 employees and more than 700 offices in more than 140 countries. It provides assurance (including financial audit), tax, consulting and advisory services to companies. The firm's history dates back to 1849 with the founding of Harding & Pullein in England. The current firm was formed by a merger of American firms Ernst & Whinney (a successor firm of Harding & Pullein) and Arthur Young & Co. in 1989. It was known as Ernst & Young until 2013, when it underwent a rebranding. The acronym "EY" was already an informal name for the firm prior to its official adoption.