The "Big Four" audit, accounting and consulting firms include: Ernst & Young, Deloitte Touche Tohmatsu, KPMG and PricewaterhouseCoopers. About.com Careers explains that they provide a range of services including public company auditing, corporate tax services, business consulting services and wealth management services.
In the 1980s, the top eight accounting and consulting firms were known as the "Big Eight." However, after a series of consolidation between firms, they became known as the "Big Five." After the Enron scandal caused Arthur Anderson to go under in 2001, the firms became known as the "Big Four."
Arthur Anderson was indicted for shredding documents in the Enron scandal. The Sarbanes-Oxley Act was passed in 2002, and it established stricter rules for auditing compliance.