Provides an in-depth study of the theory, history, practice, and interpretation of customary international law.

States often regard themselves bound by treaty rules which have developed under customary international law, even though many of the treaties themselves have not been ratified. The Law of the Sea Convention, for instance, has generated new customary rules which modified the 1958 Geneva Conventions. These & many other issues are dealt with clearly & systematically in this informative handbook on the relations between written & unwritten international law. The conclusions of the first edition of Customary International Law & Treaties were largely confirmed by the International Court of Justice in the Nicaragua Case. This fully revised second edition, while basing itself on the original version, brings the subject up to date.

Although customary international law has long been an important source of rights and obligations in international relations, there has been extensive debate in recent years about whether this body of law is equipped to address complex modern problems such as climate change, international terrorism, and global financial instability. In addition, there is growing uncertainty about how, precisely, international and domestic courts should identify rules of customary international law. Custom's Future seeks to address this uncertainty by providing a better understanding of how customary international law has developed over time, the way in which it is applied in practice, and the challenges that it faces going forward. Reflecting an interdisciplinary mix of historical, empirical, economic, philosophical, and doctrinal analysis, and containing chapters by leading international law experts, it will be of use to lawyers, judges, and researchers alike.

Customary international law, although long recognized as a primary source of international law, remains replete with enigmas, both conceptual and practical. These include how to determine the existence of opinio juris, the function of the state practice requirement, the definition of jus cogens customary norms, and the relationship between customary international law and ethics. In part because of these enigmas, the subject has generated a wide-ranging literature. However, no recent book-length work has attempted to articulate a comprehensive theory of customary international law that can effectively resolve these questions. This book sets out to accomplish this goal. Its approach is unique in a number of ways. For example, it is multidisciplinary and draws insights from fields such as legal theory, philosophy, political science, and game theory. In addition, it is anchored in a sophisticated ethical framework and explores at length the interconnections between customary international law and ethics.

Fundamentals of Public International Law, by Giovanni Distefano, provides an overview of public international law’s main principles and fundamental institutions.

Along with treaties, custom is one of the sources of international law. It is known to consist of two elements: state practice and opinio juris. While many studies have looked at traditional questions of how to identify customary law, this book takes a new and original approach. It looks instead at the structure of thought that lies beneath the arguments about customary international law. By examining these structures, the book uncovers surprising conclusions, and demonstrates what the author describes as the 'discursive splendour' of customary international law. The book guides the reader through an analysis of eight distinct performances at work in the discourse on customary international law. One of its key claims is that customary international law is not the surviving trace of an ancient law-making mechanism that used to be found in traditional societies. Indeed, as is shown throughout, customary international law is anything but ancient, and there is hardly any doctrine of international law that contains so many of the features of modern thinking. It is also argued that, contrary to mainstream opinion, customary international law is in fact shaped by texts, and originates from a textual environment. This book provides an engaging account of customary international law, whilst challenging readers to rethink their understanding of this fundamental part of the discipline.

This book seeks to re-appreciate the concept of customary international law as a form of spontaneous societal self-organisation, and to develop the methodological consequences that ensue from this conception for the practice of its application. In pursuing this aim, the author draws from three different strands of scholarship that have not yet been considered in connection with one another: First, general jurisprudential theories of customary law; second, theories of customary international law, especially as they relate to international relations scholarship; and third, methodological approaches to the interpretation of international law. This expansive, philosophical layout of the book enables the author to put the conceptual enigmas of customary international law into a broader perspective. Among the issues discussed in the book are the dichotomy of its traditional and modern forms and the respective benefits and disadvantages of inductive and deductive approaches to its ascertainment. In the course of this analysis, the author draws insights from Friedrich August Hayek’s theory of law as a ‘spontaneous order’, an information-processing device which enables the participants of a legal system to make use of decentralised knowledge. The book argues that the major advantage of custom as a source of international law lies in the fact that it is the result of a gradual process of trial and error, rather than the product of deliberate planning. This makes it a particularly apposite source of law in a time of seismic shifts in the distribution of power within a vastly diverse community of States, when a new global order is expected to emerge, the contours of which are not yet clearly discernible. This book applies general concepts of legal philosophy to explain the continuing relevance of custom as a source of international law while at the same time inferring from this theoretical framework concrete practical and methodological consequences, the most important of which is the special role that purposive interpretation plays with respect to rules of international custom. Given this broad approach, the book will be of interest to several groups of potential readers including academics interested in the philosophy of customary law in general, academic international lawyers and legal practitioners, especially judges, scholars of international relations and all those interested in how the international community of States organises itself.

Some legal rules are not laid down by a legislator but grow instead from informal social practices. In contract law, for example, the customs of merchants are used by courts to interpret the provisions of business contracts; in tort law, customs of best practice are used by courts to define professional responsibility. Nowhere are customary rules of law more prominent than in international law. The customs defining the obligations of each State to other States and, to some extent, to its own citizens, are often treated as legally binding. However, unlike natural law and positive law, customary law has received very little scholarly analysis. To remedy this neglect, a distinguished group of philosophers, historians and lawyers has been assembled to assess the nature and significance of customary law. The book offers fresh insights on this neglected and misunderstood form of law.