Examining the fulfilment of international obligations by subjects of this law, this book explores the normative and functional links between the sources and rules of international law on the one hand, and the responsibility for violating international law on the other. In the sphere of law-making, the theory of obligations allows for a more precise and considered formulation of international obligations. It has the potential to enable subjects of international law to behave more rationally, allowing deeper reflection on whether to take on obligations and how to properly perform them. This book proposes a new approach to the issue of the proper operation of international law, with the theory of obligations at its heart. Linking the institutions and concepts of international law into a rational whole, the book offers an analysis of the operation of international law and the behaviour of its subjects to develop a framework for ensuring the ultimate effectiveness of international law. Analysing sources of law including treaties and common law, alongside the resolutions of international organisations, this book demonstrates the practical application of the subject with reference to the jurisprudence of international courts and other bodies. The volume will be of interest to scholars, students, and practitioners concerned with international law – its creation, performance, application, compliance, and enforcement.