The purpose of this thesis is to map and assess the organisational and ideological development of the European Liberal Democrat and Reform party, the ELDR. More specifically, it seeks to analyse the degree of integration between the members of the ELDR over time, to identify factors that may or may not generate integration, to relate the development of the ELDR to earlier research about European parties, and finally to contribute to the ongoing debate about whether or not the traditional national party families are about to establish parties at the European level. The thesis is based on the assumption that parties adapt to their environment, in this case, the system of multi-level governance that characterises the European Union. As the European parties are composed of national parties, they are also dependent on the member parties' opportunities and motives for cooperation. If there is integration, we can, however, not only expect the European parties to adapt to their environment. As they become independent actors, they may also influence their environment. In other words, we can anticipate interaction between the European and national levels that leads to mutual adaptation, or Europeanisation. To be able to capture the interaction between the two levels, theories from international relations and comparative politics are combined. Based on interviews, participant observation, documentary research and content analysis of European election manifestos, the analyses shows that the members of the ELDR have over time reached a rather advanced level of integration, both organisationally and ideologically. Although it is possible to identify constraining factors to this development, the ELDR has, at least from what is known from literature, reached about the same level of development as the two other European parties, the Christian democratic EPP and the Social democratic PES. The internal integration of the ELDR is the outcome of a successive transfer of power from the member parties to the ELDR. By now, the ELDR can therefore be defined as a rather independent actor and as a type of party at the European level. This type of party is, however, not comparable to national parties. It is instead adapted to the institutional structure of the European Union, with, at least partly, a different organisation and different functions from those of national parties. / digitalisering@umu