The motto of the European Union, 'United in its diversity' (article IV-1, draft Treaty establishing a Constitution for Europe) serves well as the prime aspiration with regard to the quality of European legislation. The legislation of the European Union is not intended to erase the diversity of legal traditions, methods and systems in the Member States, but rather to shape their compatibility with respect for the diversity of their institutional arrangements and legal cultures. It is against this background that the quality of European legislation was discussed during a two-day colloquium organised by the Association of the Councils of State and Supreme Administrative Jurisdictions of the European Union in June 2004 in The Hague. The colloquium was attended by representatives of the 25 Member States of the EU as well as of the Court of Justice of the EC. The present book is based on the General Report written for the colloquium, the various national reports, two reports prepared by members of the Court of Justice of the EC and the Court of First Instance and the discussions. More specifically, the book deals with, inter alia, the European and national legislative process, the preliminary rulings procedure as a tool and a source for the application of European law and the various connecting links between the EU and the national legal systems. The book will not only be of interest to all persons professionally involved in the process of drafting legislation or the administration of justice, whether at the European level or in the Member States, but also to lawyers interested in legislative and jurisdictional aspects of European integration. Ernst M.H. Hirsch Ballin is President of the Administrative Jurisdiction Division of the Dutch Council of State and Professor of International Law, Tilburg University, The Netherlands. Linda A.J. Senden is Professor of European Law, Tilburg University, The Netherlands.