This book is the result of the 9th GREIT Conference on constitutional and legal pluralism in the field of international taxation. It analyses in which respect, and to what extent, national, international or supranational provisions of international tax law are subject to constitutional requirements of a different legal pedigree.rn rnThe book focuses on aspects that have not yet received much attention in legal research and thus goes beyond the now well-established fundamental freedom scrutiny of tax systems of the EEA Member States. In addition to consequences for taxpayers and courts, it covers tax policy implications. In that context, the much discussed initiatives by the OECD and the European Union on harmful tax planning and tax competition receive particular attention.rn rnThe book is divided into nine chapters treating different aspects of the above-mentioned issues. The framework is set by a first chapter on the theoretical foundations and fundamental implications of the concept of pluralism. The following chapters focus on the principles of territoriality, on non-discrimination standards, and on the fundamental freedoms. Aspects of cooperation and coordination in international tax law are discussed thereafter. Finally, an in-depth analysis of different aspects of tax competition, as well as of different concepts for the prevention of aggressive tax planning, is offered.