Big Four accounting firms

The Big Four are the four largest professional services networks in the world, offering audit, assurance, tax, consulting, advisory, actuarial, corporate finance and legal services. They handle the vast majority of audits for publicly traded companies as well as many private companies. It is reported that the Big Four audit 99% of the companies in the FTSE 100, and 96% of the companies in the FTSE 250 Index, an of the leading mid-cap listing companies.

The Big Four firms are shown below, with their latest publicly available data.

This group was once known as the "Big Eight", and was reduced to the "Big Six" and then "Big Five" by a series of mergers. The Big Five became the Big Four after the fall of Arthur Andersen in 2002, following its involvement in the Enron scandal.

Other large professional services networks include BDO, RSM, Mazars, Grant Thornton, Crowe Horwath, HLB and Clifton Larson Allen.

None of the Big Four firms is a single firm; rather, they are professional services networks. Each is a network of firms, owned and managed independently, which have entered into agreements with other member firms in the network to share a common name, brand and quality standards. Each network has established an entity to co-ordinate the activities of the network. In one case (KPMG), the co-ordinating entity is Swiss, and in three cases (Deloitte Touche Tohmatsu, PricewaterhouseCoopers and Ernst & Young) the co-ordinating entity is a UK limited company. Those entities do not themselves perform external professional services, and do not own or control the member firms. They are similar to law firm networks found in the legal profession.

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