In November 1991 the EC acceded as a member of the FAO. On January 1, 1995 the EC became an original member to the WTO. This study deals with the interaction of two legal systems, namely between the legal system of the Community and that of other IOs. The more powers the Community gains, the more important it becomes to enable the Community to exercise these powers within the framework of relevant IOs. In particular, where the subject concerned comes under the Community's exclusive competence, the Member States have transferred their powers to the Community and thus the competent actor is the Community itself. The subject of participation by the Community in other IOs is not as yet well regulated either under Community law or under international institutional law. Furthermore, it has not been extensively treated in the literature to date. Hence, this study offers a theoretical analysis of the subject as well as an examination of daily practice in three case-studies on the relations of the EC with the FAO, the ILO and Fisheries Organizations, in particular the NAFO.