1. Deloitte, Ernst & Young (EY), KPMG, and PricewaterhouseCoopers are the four largest professional services networks in the world together known as "The Big Four." (PwC).
2. The four are frequently grouped together because they have similar sizes to the rest of the market in terms of personnel and income, and they are viewed equally in terms of their capacity to offer a broad range of professional services to their clients. 
3. Due to the regularity with which these organisations interact with Fortune 500 corporations, they are equally appealing networks to work in among people seeking to launch a career in professional services, particularly accounting.