This article examines the organisation and strategies of Belgian interest groups and their European peak-organisations with respect to the EU policy-making arena. It conceptualises the European Union as a of multi-level governance political system that consists ofmultiple interlocking government levels (sub-national, national and supranational), governed by means of non-hierarchical actor configurations with a blurred boundary between the public and the private sphere. It further argues that the European policy-making can best be studied from a (historical) new-institutionalist perspective which emphasises that the preferences andthe behaviour of political actors are shaped by the institutional context which provides opportunities and constraints. Evidence of the institutionalfactors within a multi-level governance setting is then given from the organisational structure and strategies of Belgian interest groups in general and from the environmental policy sector in particular.