Mergers, acquisitions and takeovers are terms that need to be distinguished, but in both domestic and foreign literature, these terms are often indistinguishable and used synonymously. There are various motives for companies to opt for the merger or acquisition process, and synergistic effects are the main reason for this. If the company does not want to be taken over, there are strategies in place to defend against potential takeover, but the bidder can also use certain strategies to acquire the desired company. In order for the takeover process to be successful, all stages of the process must be completed successfully. In addition to presenting the theoretical part, the idea of the paper is also to investigate how successful the mergers and acquisitions of selected airlines in Europe are based on the data available before and after the mergers and acquisitions. The paper also investigates the correlation of the size of the company with the merger and acquisition, ie investigates whether more often the subject of merger is the same size of the company and the subject of acquisition of the different size. The research has shown results that show an increase in the success of the company after the merger and acquisition. The assumption that companies merged are the same size proved to be partially correct. The obtained research data indicate a positive correlation between mergers of companies of different sizes.