This chapter provides an overview of competition law and its economic context. Section 2 describes the practices that competition laws attempt to control in order to protect the competition process. Section 3 examines the theory of competition and gives an introductory account of why the effective enforcement of competition law is thought to be beneficial. Section 4 considers the goals of competition law. Section 5 introduces two key economic concepts, market definition and market power, that are important to a better understanding of competition policy. The chapter concludes with a table of market share figures that are significant in the application of EU and UK competition law, while reminding the reader that market shares are only ever a proxy for market power and can never be determinative of market power in themselves.