This paper applies a novel methodology to a unique dataset of large concentrations during the period 1990-2002 to assess merger control’s effectiveness. By using data gathered from several sources and employing different evaluation techniques, we analyze the economic effects of the European Commission’s (EC) merger control decisions and distinguish between blockings, clearances with commitments (either behavioral or structural), and outright clearances. We run an event study on merging and rival firms’ stocks to quantify the profitability effects of mergers and merger control decisions. We back up our results and methodology by using alternative measures for the merger’s profitability effects based on balance sheet data and obtain consistent results. Our findings suggest that outright blockings solve the competitive problems generated by the merger. Remedies are not always effective in solving the market power concerns, at least not on average. Nevertheless, both structural (divestitures) and behavioral remedies do help restore effective competition when correctly applied to anticompetitive mergers during the first investigation phase. Yet, they are on the whole ineffective or even detrimental when applied after the second investigation phase. Finally, remedies - especially behavioral ones - seem to constitute a rent transfer from merging firms to rivals when mistakenly applied to pro-competitive mergers.