List the Big Four accounting firms.

The Big Four refers to the the four largest professional services networks in the world. It consists of Deloitte, Ernst & Young (EY), KPMG, and PricewaterhouseCoopers (PwC). 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.