The thesis examines the potential for international institutional isomorphism by using EU enlargement as a most-likely-case scenario. Focusing on EU social policy as an area where nonstate actors are likely to exercise pressure across national boundaries, the thesis distinguishes three types of diffusion pressures: 1. transposition of EU secondary legislation; 2. coordination through mutual adjustment of practices; 3. imitation of successful practices and/or propagation of favored models by societal actors. Network analysis of relations between EU, government, and nonstate organizations, in particular labor and employer organizations, will shed light on the types, direction, and density of interactions in order to determine the relative importance of different actors in the diffusion process. The project hypothesizes that the degree to which different organizations have Europeanized their network contacts constitutes an important explanatory variable for their role in the diffusion process.