Taking the cases of the Swedish and the Polish women’s movements and their relation to the European Union as examples, this thesis studies national-level social movements adapting to international structures. The European Union has become an important arena for international politics. In order to push for their interests many social movement actors desire a presence in Brussels. To do so, however, they need to adapt to the European Union multi-level governance system by speaking with one voice. As this thesis demonstrates, at the national level this adaptation may entail a number of organizational challenges. The study explores the challenges involved when a new layer of organization is added to a social movement. Eva Karlberg is a sociologist at Södertörn University. This study is her doctoral thesis, written within the research area of Politics, Economy and the Organization of Society (PESO) and the Baltic and East European Graduate School (BEEGS).