In this paper, we have shown that the operations of Mergers and Acquisitions (M&A) are necessary for the growth of banks and for passing to increase the scale of returns. The empirical results have confirmed this affirmation. The time has had a negative effect on efficiency while the dummy M&A variable has had positive effects. The composite mergers-time variable has had positive effects, which means that in the long run the M&A achieve all their aims. Our study, therefore, is the first to analyze the dynamic effects of mergers on bank performance derived from both the acquisition of another bank and time, using panel data methodology, for the period 2005-2013, in a sample of 60 acquire banks, in 17 European countries.