Öz In this article, the enlargement process of the European Union, rather than deepening process of the Europe is studied. In an historical perspective, the performances of an old member, Greece, a new member, Poland and an accession country, Turkey are compared and analysed in fulfilling the EU's political criteria. The other purpose of the study is to investigate the reasons why the EU is hesitant for Turkey's membership while the countries with similar conditions are already accepted as members. Greece, despite the political instability at the time of accession, joined the EU by using the advantages of her historical, cultural and geographical proximity to Europe as well by the EU's encouraging support. Similarly, an old communist country, Poland is now a member again with more or less similar reasons. However, the fiı ct that Turkey with similar conditions is still not a member supports the claim that the EU does not seem to treat Turkey on an equal base.