The thesis examines the impacts of European integration on interest representation in an EU applicant country, Hungary. The study identifies and explores the mechanisms of Europeanisation and their effects on the organisation and functioning of interest groups and of interest representation structures. The study primarily uses the qualitative method. The empirical part consists of three detailed case studies, covering the pharmaceutical sector, the agricultural sector, and peak employers' associations. The research is largely based on primary data gained from interviews and documents. Each case study explores the inclusion of Hungarian interest groups in the European level of interest representation, their participation in EU-related policy-making, and the European policy impacts on group developments and interest representation structures. The theories of Europeanisation constitute the primary analytical framework for the study. In addition in an attempt of contextualisation, the theories of political and economic transition and consolidation are also examined. The empirical chapters indicate a variation in the forms and degree to which Europeanisation affected interest representation in Hungary. Sectoral, group and interest representation structure characteristics, and the nature of the EU level interest representation are examined as the variables responsible for the differences. The research findings point to the need to distinguish between formal and substantive Europeanisation. It is also argued that Europeanisation is closely intertwined with and embedded in the double process of political and economic transition and consolidation in the Central and Eastern European context