||My work presents the study of the cross-border mergers and acquisitions. I discuss this phenomenon in two ways - from the empirical point of view and from the theoretical point of view. The data shows that most of the foreign direct investments is in the form of mergers and acquisitions (M\&As) and that merger waves can be identified. Also we can see that economic integration gives incentives toward more M\&As and that the inequality between individual deals increase. Model of cross-border M\&As as a instruments of comparative advantage and model with heterogeneous productivity try to explain previous facts. The fact, that the firms prefer developed countries to developing countries suggest that the process of decision about M\&As is influenced by infrastructure and quality of legal system of target country. The model of incomplete contracts with heterogeneous products and productivity study this influence for the case of vertical M\&As. I try to explain that however the M\&As increase the value of the shares, they are often unprofitable, by the model of preemptive M\&As at the end of the work.