Deloitte is a privately held multinational professional services network headquartered in London, United Kingdom. Founded in 1845 by William Welch Deloitte, the firm pioneered independent auditing and has since grown into one of the "Big Four" accounting firms. Deloitte operates through a network of member firms under Deloitte Touche Tohmatsu Limited (DTTL), a UK private company limited by guarantee. The organization provides services in audit, consulting, financial advisory, risk management, tax, and legal across more than 150 countries. As of 2025, Deloitte employs thousands of professionals globally and reported annual revenues of $70.5 billion. The firm is known for its decentralized structure, with each member firm legally independent.