http://en.wikipedia.org/wiki/Big_Four_%28audit_firms%29
The
Big Four are the four largest international
professional services networks in
accountancy and
professional services,
offering audit, assurance, tax, consulting, advisory, actuarial,
corporate finance and legal services. They handle the vast majority of
audits for
publicly traded companies as well as many
private companies, creating an
oligopoly
in auditing large companies. It is reported that the Big Four audit all
but one of the companies that constitute the FTSE 100, and 240 of the
companies in the FTSE 250, an index of the leading mid-cap listing
companies.
[1] The Big Four firms are shown below, with their latest publicly available data.
KPMG, PricewaterhouseCoopers, Ernst and Young, and Deloitte.