The Big Four:

The Big Four is the nickname used to refer collectively to the four largest professional services networks in the world.

Deloitte:

Deloitte Touche Tohmatsu Limited, commonly referred to as Deloitte, is a multinational professional services network with offices in over 150 countries and territories around the world. Deloitte is the ranked 1 accounting firm

PwC: PricewaterhouseCoopers

PricewaterhouseCoopers is a multinational professional services network of firms, operating as partnerships under the PwC brand. PwC is the ranked 2 accounting firm.

EY: Ernst & Young

Ernst & Young Global Limited, doing business as EY, is a multinational professional services network with headquarters in London, England. EY is the ranked 3 accounting firm

KPMG: Klynveld Peat Marwick Goerdeler

KPMG International Limited is a British-Dutch multinational professional services network. KPMG is the ranked 4 accounting firm