This dissertation gauges the influence of regions from EU decentralized member states on European policies. The ability of regions to shape EU decisions has been at the center of discussions on European integration theory and of EU politics for fifteen years now. By combining evidence from German, Italian, and Spanish federalism (and from two EU policy areas - audiovisual and cohesion), the author shows why and when understanding EU policies requires taking regional lobbying of the European Parliament and the Commission into consideration. This first attempt to combine the literature on "The Europe of the Regions" and on multi-level governance with policy analysis will be illuminating for scholars and practitioners interested in the EU decision-making process, as well as for those concerned with Europeanization. Dissertation.