This in-depth analysis covers the history of the EU Merger Control as well as its jurisdiction, thus focusing on the European Commission Merger Regulation (ECMR) and its importance and application in complementing Articles 81 and 82 of the EC Treaty (Treaty of Rome) which by themselves were considered inadequate to control mergers. The ECMR gives the European Commission (EC) jurisdiction to cover mergers, acquisitions and full-function joint ventures with economic impact beyond the territory of a Member State. The study also offers a substantive assessment as to the potential competition impediment and existing procedural issues and judicial reviews of EU merger decisions. Effectively, the ECMR provides a ‘one-stop shop’ to the benefit of the EC who has exclusive jurisdiction to examine concentrations with a Community dimension to the exclusion of national competition authorities (NCAs) in the Member States. Where the relevant jurisdictional thresholds are not met, NCAs will examine concentrations under their own national merger control rules. The mechanisms put in place by the ECMR to maximise the benefits of this 'one-stop-shop' principle thus ensure that the best-placed authority reviews a concentration. Ultimately, the Commission has the power to block those mergers that it determines would ‘significantly impede effective competition, in the common market or in a substantial part of it, in particular as a result of the creation or strengthening of a dominant position’.