The aim of this thesis was to study the Baltic Sea Region (BSR) Programme and the North Sea Region (NSR) Programme within the Transnational Interreg IV B Programme for the period 2007-2013, by making a comparison between Sweden and Denmark. The thesis looked at the level of involvement of both National Planning Authorities in the designing process of the programmes and projects, and investigated whether the Interreg programmes influence the authorities in their work with future policy-making, and the national spatial planning policies in general. The ambition of the thesis was also to clarify the links between the Interreg Programmes, the ESDP document, the Territorial State and Perspectives of the European Union and the Territorial Agenda, and how these documents have influenced the EU Territorial Cohesion debate and the creation of the EU Baltic Sea Strategy. The reason was to better understand the role of the National Planning Authorities in the implementation of the transnational programmes and their work towards territorial cohesion. The methods used for the thesis consisted of secondary research and analysis of the intergovernmental “Territorial Documents”, the Interreg programmes and their specific projects, and not least, the study of books, articles, and other documents and sources of interest for this topic. Interviews were made with people working at Swedish “Boverket”, Danish “By- og Landskabsstyrelsen” (BLST) and “Danske Regioner” (Danish Regions). Some of the main findings have been the different approaches among the Planning Authorities towards their potential leadership in the Interreg projects, the little time dedicated to the Interreg work in general at Swedish Boverket, and Boverket’s scarce intervention in the development-process of the EU Baltic Sea Strategy. On the Danish side there is very little priority given to the diffusion and transfer of knowledge, while in Sweden on the other hand, this is one of the main issues for all the authorities involved. The conclusion is that, even if Sweden and Denmark are close neighbours and are collaborating in many fields, there are some substantial differences in attitude and action towards their role as participators of the Transnational Interreg projects, differences which, if emphasised, could be useful knowledge for both parts in order to develop their own Interreg-work, responding to the growing interest of the EU in territorial concerns.