An ever growing European Union (EU)? Treaty reforms, EU-budget negotiations and Euro-zone enlargements: European integration was put to a great test at the beginning of the 21st century. How were these developments and especially the way to the Lisbon Treaty experienced in different EU member states? How did the variety of actors in seven exemplified countries react to these changes and a growing heterogeneity within the EU? How did they thus formulate their ideas for the future of the Union, their Leitbilder? The approach of this research originates in the basic assumption that Leitbilder can be seen as a key factor in the development of the EU. Such Leitbilder contain conceptual statements dealing with the underlying institutional and constitutional construction of the EU and its potential finalité. They can also relate to elements of the integration process, for example specific policy areas. The analysis of Leitbilder in old and new EU member states answers the questions in which way the spectrum of the Euro-political Leitbilder changed with enlargement and if, as a consequence of potentially increasing heterogeneity within the EU, there are foreseeable tendencies of greater fragmentation, continuity or reinvention.