The main issue of this book is to analyze whether and to what extent EU membership affects the implementation and application of binding decisions of International Organizations in the domestic legal order of EU Member States. It also examines how the decisions of the EU adopted in the II. and III. pillar vis- -vis its Member States are to be qualified. Are they also decisions of an IO or are they decisions comparable to Community law measures? Thus, this book provides useful insights into the interaction of decisions of IOs with the European and the national legal orders, comparing the situation in Germany, the Netherlands and France.