Chapter 6 allows Christian Ahlborn, together with Will Leslie, to revisit his earlier analytical critique of market investigations in UK competition law (published in Ten Years of UK Competition Law Reform, Dundee University Press, 2010), in a chapter entitled, ‘ “Jack of All Trades, Master of None”: The Ever-increasing Ambit of the Market Investigation Regime!’ Whereas the beginning of the decade saw the National Audit Office criticizing the market investigation regime’s low profile, market investigations had figured amongst the Competition and Markets Authority’s most high-profile interventions by the end of it. This chapter considers the extent to which this unique UK competition policy instrument has simultaneously undergone significant legislative reform as well as a slew of judicial challenges. These events have undoubtedly matured the regime and put its procedures on a firmer statutory footing. However, the same question posed in 2010 has not yet been fully answered: as set out in this enlightening chapter, in the authors’ view, it still remains unclear just what market investigations are actually for.