This chapter analyses the relationship among competition law and the various sectoral regulatory regimes making up the EU body of economic regulation, at the systemic, substantive and institutional level. In the light thereof and of experience with comparable tools in other jurisdictions, it makes recommendations regarding the interplay between market investigations and sector-specific regulation. In our opinion, market investigations could easily be integrated in the existing body of EU economic regulation. At the systemic level, this new instrument should have a horizontal scope and hence be applicable to regulated sectors, to usefully close eventual regulatory gaps. At the substantive level, it should rest on economic knowledge and methodology, in line with existing EU economic regulation, yet without being straitjacketed within specific competition law analysis. At the institutional level, a close transversal cooperation between the Commission and the relevant NRA(s) is needed at every stage of a market investigation implementation, if and when it is applied in regulated sectors.