Numerous Security Council Resolutions, WTO Appellate Body rulings, Association Council Decisions, judgements of the ECrtHR have to be implemented by the EU Member States according to their constitutional provisions. However, the fact that the EU is often member of those IOs or has acquired certain competences means that also the EU is, within the limits of its competences, required to implement those decisions. In this way the legal characteristics of those decisions is modified in the sense that they obtain Community law features such as supremacy and direct effect. 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 IOs 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-à-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.