Structural and geopolitical changes in Europe and the European integration process have promoted cross-border co-operation (CBC) in Europe. Initiatives from the European Union like the Interreg programme have even accelerated this development. But successful cross-border co-operation needs an adequate political framework to function and evolve.In this essay various forms of political cross-border co-operations by way of two case studies will be discussed. The two case studies represent a special position in comparison with other cross-border regions in Europe: They are both cross-border regions within the European Union; they are densely populated with 3.6 resp. 6.4 Mio. inhabitants or 170 resp. 145 inhabitants per km (EU 25: 115 inhab/km) and in both areas are two major cities. Both respective cities are considered as MEGAs (Metropolitan Growth Area) by the ESPON 1.1.1 project and are very close situated to each other (Copenhagen-Malmö 25 km,Vienna-Bratislava 50 km “as the crow flies”), but also were somehow separated until recently (Closed borders between Austria and Slovakia until 1989, no fixed link over the Öresund strait until 2000). Besides that, the further integration of Europe through the European Union also became a driving force for closer co-operation in cross-border regions. The EU-accession of Austria and Sweden in 1995 and of the Czech Republic, Slovakia and Hungary in 2004 is crucial for the case areas. So, successful co-operation needs an adequate political framework. Hence a certain political cross-border co-operation is necessary for a successful integration and a possible increase of competitiveness of the cross-border region. Both parts, co-operation as the framework for integration and integration as the motive for co-operation are highly depended on each other and influence the further development of the cross-border region. The next two chapters will provide an abstract on the current development in the two case areas regarding their approach to political cross-border co-operation and the progress of cross-border integration and exchange. This essay is based on my thesis completed in May2006 to finish the master degree in spatial planningat the Vienna University of Technology.