The chapter assesses the possible role of market investigation endowed with broad remedies, when a market suffers from competition problems and infringement cases under competition law provisions are infeasible or ineffective. It lays out a number of theories of harm, i.e., reasons why certain market features or behavior by market participants may lead to consumer harm compared to a relevant counterfactual. It identifies theories of harm in markets (i) where none of the firms is dominant and (ii) with a dominant firm but article 102 TFEU is not effective or applicable or (iii) a dominant firm may arise. It also argues that the European Commission should look for simple “intervention triggers” for a market investigation. While some of the identified harms are more likely or more pronounced in digital markets, a presumption that market investigations primarily addresses competition problems in digital markets is misguided. Finally, when sector regulation is, in principle, applicable, market investigations may fill a gap between standard competition tools and sector regulation.