This chapter describes the UK system of market studies and market investigation references. It begins by describing the CMA’s ‘general function’ of gathering information about markets, followed by an explanation of what is meant by a ‘super-complaint’. It examines the purpose, procedure and outcomes of market studies, including possible outcomes. Market studies sometimes lead to market investigation references, although there are several other possible outcomes of a market study. The chapter describes the making and determination of analyses and the market investigation provisions under Part 4 of the Enterprise Act 2002. Having briefly considered public interest cases, enforcement and other supplementary matters, the chapter discusses how the market investigation provisions have been working in practice. The final section of the chapter briefly refers to the enforcement and review of undertakings and orders still in force under the monopoly provisions in the former Fair Trading Act 1973.