The German political foundations (politische Stiftungen) have played an important role facilitating party cooperation in countries in transition from authoritarian rule and, more recently, in the context of the transformation of Central and Eastern European Countries (CEEC). As party-related, publicly financed and largely autonomous organisations, these foundations are specific transnational actors. This chapter deals with both theoretical and empirical aspects of the study of EU enlargement, focussing particularly on the party cooperation preceding the accession of new member states. An analysis of the transnational cooperation between the European party federations and the political foundations in the years preceding the accession of new member states to the EU helps us to reconsider the questions of identity and transnational socialisation in an enlargement context.