This chapter provides an account of the market investigation provisions on the UK Enterprise Act of 2002, which enables the Competition and Markets Authority (CMA) to investigate markets and to determine whether any ‘features’ of a market prevent, restrict or distort competition. If the CMA discovers an ‘adverse effect on competition’, powers are available to achieve as ‘comprehensive solution as possible’ through the imposition of remedies, up to and including mandatory divestiture. This chapter describes these powers, explains the institutional regime within which decisions are made and the procedure that the CMA follows in market investigation cases. Some other jurisdictions possess similar powers to those contained in the Enterprise Act. In particular, the chapter describes the powers available to the competition authorities in Greece, Iceland, Mexico and South Africa.