Big Four accounting firms

The Big Four are the four largest professional services networks in the world: Deloitte, EY, KPMG, and PwC. The four are grouped because of their large sizes relative to their competitors, both in terms of revenue and workforce headcount; they are likewise considered comparable in their ability to provide consistent and reliable professional services to their clients. Colloquially, their networks are considered of parity to those seeking careers in the services offered by these firms because of the frequency with which they engage with Fortune 500 companies.

Source: Wikipedia — Big Four accounting firms (CC BY-SA 4.0)