We estimate the deterrence effects of European Commission (EC) merger policy instruments over the 1990-2009 period. Our empirical results suggest that phase-1 remedies uniquely generate robust deterrence as-unlike phase-1 withdrawals, phase-2 remedies, and preventions-phase-1 remedies lead to fewer merger notifications in subsequent years. Furthermore, the deterrence effects of phase-1 remedies work best in high-concentration industries; i.e., industries where the HHI is above the 0.2 cutoff level employed by the EC. Additionally, we find that phase-1 remedies do not deter clearly pro-competitive mergers, but do deter potentially anti-competitive mergers in high-concentration industries. (JEL K21, K40, L40) * Corresponding author. For helpful comments and suggestions, we wish to thank Jozsef Molnar from DG-Comp and participants at the Barcelona IO Workshop, European Commission's DG-Comp, IIOC in Chicago, IFO Institute in Munich, MaCCI Conference in Mannheim, TILEC seminar at Tilburg University, and University of Alicante. 2