Mergers and acquisitions transactions have become an almost everyday feature of economic life. However, according to some studies approximately 50% of such transactions do not bring expected results. According to other studies, only some one third of mergers can be considered successful. This article is an attempt to explain why companies merge despite such a high failure risk for this type of transactions. The reasons for mergers and acquisitions have been presented in a breakdown into three major groups: the reasons of owners and managers, market and marketing reasons and financial reasons. Such a breakdown allows for a detailed analysis of particular factors making up the final decision to merge with another firm. Obviously, the hierarchy and rank of specific reasons for mergers and acquisitions has been changing over years. Nevertheless, merger transactions always constitute a deliberate and effective strategy for maintaining or speeding up the growth rate of a company, strengthening its market position or rationalising costs. For companies they are often the only effective way to survive on the world market and to face international competition. Therefore, irrespective of the frequently voiced opinions that mergers motivated by prevailing trends are carried out without sufficient justification, and the costs involved exceed by far the possible gains, such transactions are still to be the case to a greater or smaller extent.