In response to a climate in which respect for international law and the law of the European Union is rapidly losing ground, Paul Gragl advocates for the revival of legal monism as a solution to potentially irresolvable normative conflicts between different bodies of law. In this first comprehensive monograph on the theory as envisaged by the Pure Theory of Law of the Vienna School of Jurisprudence, the author defends legal monism against the competing theories of dualism and pluralism. Drawing on philosophical, epistemological, legal, moral, and political arguments, this book argues that only monism under the primacy of international law takes the law and the concept of legal validity seriously. On a practical level, it offers policy-makers and decision-makers methods of dealing with current problems and a means to restore respect for international law and peaceful international relations. While having the potential to revive and elicit further interest and research in monism and the Pure Theory of Law, the comprehensiveness and scope of the book also make it a choice text for inter-disciplinary scholars.