Just how International and European Community Law is being integrated into domestic legal systems is as yet not too well known. To gain a clear overview of this grey area requires more than knowing about the various constitutional rules. What is also needed is a study of little-known administrative practices and the attitudes of the national courts, where case-law is often as complex as it is diverse. When all these elements are taken into account, the general picture that emerges is a much more subtle one, transcending the classical positions based on the theories of monism and dualism. To grasp this reality and go beyond preconceived ideas, it seemed indispensable to make a thorough analysis of national practices. To this end, the International Law Centre of the University of Paris XIII (Cedin Paris XIII) took the initiative, in 1990, of setting up a network of European international lawyers to work on the theme `International norms and legal barriers'. This book presents the outcome of the network's programme. The research was organized on the basis of a single questionnaire which provided the outline of a common workplan, to which each of the contributors has adhered. Detailed comparisons of national practices can now be made, relating in particular to international treaties, acts of international organisations and of the European Communities, and to unwritten international law. This is the first time that such a comprehensive and detailed survey has been made of all thirteen countries. Reading the national reports one after the other provides complete information on domestic practices; reading them crosswise gives a direct comparison between the different countries on specific issues.