Resumen
The literature devoted to the EU often points out its hybrid side, which is in the process of constant transformation. The process is comprehensive, in the economic, political, military and safety domain. This complex task is not timed, because it is considered a process and not a one-time act. The original idea that social changes have evolutive development and need time to become quality changes is not abandoned. Although today's EU environment is drastically changed compared to the late fifties of the last century, the main reasons for a country to join the EU have remained virtually the same. All of these reasons basically refer to the same aspirations of potential candidate countries for membership: economic, political, safety, cultural and others. Possession of an appropriate macroeconomic model and relatively useful statistical data is a conditio sine qua non of a successful analysis of the benefit and the cost of joining the EU. Key words: accession process, EU, accession effects, Cecchini report, empirical models of accession.