Written by renowned historians from the six founding countries of the EEC, the here presented work aims at taking stock of the unification process which has been going on now for 50 years. Starting out from the Treaties of Rome and also viewing at the treaty signed in Lisbon at the end of 2007, the authors do not only describe the main phases of the process but furthermore emphasize the challenges for the European unification project. At the beginning, they particularly emphasize the restructuring of Europe by way of the Treaties of Rome, to then show progress and difficulties of integration and to finally think about the prospects of a European political union. All phases of the European construction are looked at in their respective historic context. Thus, this work is essential for the understanding of the many European questions. At a time when difficulties become more and more and many contemporaries doubt that the European construction makes sense, the authors intend their work to be a contribution to a still current debate. This scientific work is the result of the joint work of a group of historians under the direction of Marie-Therese Bitsch, Professor at the Robert Schuman University in Strasburg and a renowned specialist of the history of European integration.