EN
This article discusses deepening of European integration resulting from the reforms of eurozone in the context of the Optimum Currency Areas (OCA) theory. The paper begins with an outline of the OCA theory crucial findings. The second section discusses the importance of proper selection of monetary union membership criteria. Next, the deepening of the European integration in light of the endogeneity of currency area optimality hypothesis is discussed. The final section emphasizes possible changes in the balance of costs and benefits of monetary integration for countries that have not yet fulfilled the necessary conditions for the adoption of the euro.