This book has been written in the belief that much disagreement in international legal discourse is theoretical. As Steven Ratner and Anne-Marie Slaughter observe in their introduction to the volume The Methods of International Law ‘beneath the surface of much scholarship ... are a host of unanswered questions about presuppositions, conceptions, and missions, all of which influence ... analysis of an issue and ... conclusions and recommendations for decision makers’. There are few occasions to clarify the ‘presuppositions, conceptions, and missions’ because explicit theorization is still the exception and unspoken theory tends to occlude arguments pertaining to the underlying epistemological and ontological premises. It is not as if there are not enough theories of, or about, international law. But these are not subjects of sustained debate and reflection. A focus on theory is also necessitated today by the growing ‘specialization and fragmentation’ of the field of international law.