The fifth enlargement round (Enlargement) of the European Union (EU), which took place on May 1st 2004, is rightly recognized to be a momentous landmark in the history of modern European integration; the culmination of a fifteen-year process that has variably transformed and will continue to deeply impact the regime characteristics of the post-communist New Member States (NMS) and the remaining candidates (Bulgaria, Croatia, Romania and Turkey) - as well as the EU governance system and its perception of itself as an international actor.