The Big Four are the four largest professional services networks in the world: Deloitte, EY, KPMG, and PwC. They are the four largest global accounting networks as measured by revenue. The four are often grouped because they are comparable in size relative to the rest of the market, both in terms of revenue and workforce; they are considered equal in their ability to provide a wide scope of professional services to their clients; and, among those looking to start a career in professional services, particularly accounting, they are considered equally attractive networks to work in, because of the frequency with which these firms engage with Fortune 500 companies.
The Big Four all offer audit, assurance, taxation, management consulting, valuation, market research, actuarial, corporate finance, and legal services to their clients. A significant majority of the audits of public companies, as well as many audits of private companies, are conducted by these four networks. Until the late 20th century, the market for professional services was dominated by eight networks which were nicknamed the "Big Eight". The Big Eight consisted of Arthur Andersen, Arthur Young, Coopers & Lybrand, Deloitte Haskins and Sells, Ernst & Whinney, Peat Marwick Mitchell, Price Waterhouse, and Touche Ross.
