Deloitte Touche Tohmatsu Limited, commonly referred to as Deloitte, is an international professional services network headquartered in London, England.

The firm was founded by William Welch Deloitte in London in 1845 and expanded into the United States in 1890. It merged with Haskins & Sells to form Deloitte Haskins & Sells in 1972 and with Touche Ross in the US to form Deloitte & Touche in 1989. In 1993, the international firm was renamed Deloitte Touche Tohmatsu, later abbreviated to Deloitte. In 2002, Arthur Andersen's practice in the UK as well as several of that firm's practices in Europe and North and South America agreed to merge with Deloitte.Subsequent acquisitions have included Monitor Group, a large strategy consulting business, in January 2013. The international firm is a UK private company, limited by guarantee, supported by a network of independent legal entities.