The agglomeration area of the city of Vienna is growing and the administrative borders are losing their significance. The inhabitants of such an agglomeration or metropolitan area consider themselves as a part of the metropolitan area and not only their specific area. While the people are living a “metropolitan life”, the political and administrative levels do not reflect this trend. This can be observed particularly in the transition area between the city and the surrounding municipalities. In order to combat the problems brought about by this development, the planning instrument “Regionale Leitplanung” (English: “regionally based lead planning”) was developed and carried out in the metropolitan area of Vienna. The co-operation between different political and administrative levels is a key element of this instrument. The very first “Regionale Leitplanung” was implemented in the northern area of the metropolitan Vienna and the second in the south in the Lower Austrian district of Mödling. The first section of this thesis contains an in-depth observation of the theoretical basis of co-operations between cities and their surrounding municipalities and agglomeration areas in general. Depending on the country and culture, there are different levels of such co-operations, as well as different methods used to define the agglomeration areas. Since the focus of this thesis is on the metropolitan area of Vienna, some statistical data is shown to create an overview. This section is followed by the introduction of the most important existing co-operations in the Viennese metropolitan area. The main focus of this thesis is an analysis of the two completed processes. The basis of this analysis was achieved through interviews with representatives of the administration, experts and politicians. The goals of the analysis were to determine the achievements of these processes and the added value for the regions, to detect problems before, throughout and in the concluding implementation phases of the processes. Furthermore, the results of the analysis helped to estimate the qualification of this instrument for co-operations between cities and their surrounding municipalities. It can be concluded, that the processes were successful, as they helped to convey a consciousness of regional thinking and also induced further co-operations, processes and concepts in the regions. In the “Regionale Leitplanung” in the north of Vienna, the process was used to discuss and co-ordinate the contents of the legally binding regional spatial plan (“Regionales Raumordnungsprogramm”) which had to be renewed. All actors benefitted from this method, as the municipalities were given the chance to discuss and question every detail, and the national government was more efficient in the actual reviewing work later on. Nevertheless, there is potential for improvement in future implementations. This potential is expressed in proposed actions, which can contribute to the continuing and further development of this instrument. The thesis is concluded with ideas and visions of how co-operations between the city and its surrounding municipalities in the metropolitan area of Vienna could be rearranged to be more effective. The author is convinced that it is absolutely necessary to encourage inter-communal co-operations and regional thinking in agglomeration areas of growing cities for successful urban development.