The chapter provides an overview of the structure of the accounting profession and the audit marketplace, and identifies the professional bodies and the roles of the key watchdogs (FRC, Insolvency Service and FCA). The scale of the sector and its structure is discussed. The chapter covers the consequences of EU changes to the audit, embodied in the Audit Reregulation and Directive, including audit rotation, the 70% cap on non-audit fees and blacklisted work. Audit is but a small part of the Big Four’s workload, and the chapter examines the structure of the Big Four firms including their consultancy divisions. Audit fee income and the role of tendering is examined.