With a century of solid theory behind it, tax law confronts a new reality: the weakening of the tenacious link between the sovereignty of states and taxation. Yet it is to the continuity of certain themes and principles inherent in the various national tax systems that tax law scholarship continues to look, even as it develops new principles designed to meet the expanding processes of internationalization. This completely updated collection of essays offers an expert comparative analysis, conducted by a sample of the best international tax law scholars, of the fundamental theory of tax law and of the prospects in the near future of tax legislative systems. The emphasis falls naturally on tax theory, jurisprudence, and legislative development in the Member States of the European Union (particularly in Italy, Germany, and Spain), where the process of tax harmonization has been under way for many years. The effect of these processes, via the relevant tax treaties, on the tax systems of Japan and the United States provides a secondary emphasis. Practitioners and academics in tax law will find in this book an invaluable understanding of the challenges that tax law theory strives to meet at this crucial moment in economic history. The essays present a full and reliable exposition of the current theoretical approaches adopted by the various schools of thought in the field, as well as of the main contributions of jurisprudence.