The article deals with the role of "efficiencies" that may result from mergers, particularly vis-à-vis their trade-off with mergers' anticompetitive effects. The analysis, whose starting point is the strong criticism expressed by authoritative American jurists and economists to recent decisions of the European Commission, devotes special attention to the December 2002 Proposal presented by the Commission to revise the existing merger regulation (Reg. no. 4064/89). Said Proposal, and the contextual "Draft Notice" "on appraisal of horizontal mergers" confirm that the EU has evolved towards a positive evaluation of efficiency-enhancing transactions "within" a traditional competition policy that - via the concept of "dominance" - is influenced by the "structure-conduct-performance" paradigm. This leads the analysis to further focus on the existing (although sensibly reduced) differences between the American and European approaches, as well as on the conceptual foundations underlying the European position, with reference to both its economic "rationale" and its historical (political) roots: hence rejecting the blunt characterization of European merger law and policy as merely "protecting the inefficient competitors" often affirmed by U.S. critics.