Two fish are swimming in a pond. "Do you know what?" the fish asks his friend. "No, tell me." "I was talking to a frog the other day. And he told me that we are surrounded by water!" His friend looks at him with great scepticism: "Water? What's that? Show me some water!" This book is an attempt to stir up 'the water' the two fish are swimming in. It analyses the different theoretical approaches to international law and invites readers to engage with legal thinking in order to familiarize ourselves with the water all around us, of which we hardly have any perception. International lawyers and students of international law often find themselves focused on the practice of the law rather than the underlying theory. The main aim of this book is to provide interested scholars, practitioners, graduate, and postgraduate students in international law and other disciplines with an introduction to various international legal theories, their genealogies, and critique. By providing an analytical approach to international legal theory, the book encourages readers to sharpen their sensitivity to these different methodologies and to consider how the presuppositions behind each theory affect analysis, research, and practice in international law. Theories of International Law is intended to assist students, scholars, and practitioners in reflecting more generally how knowledge is formed in the field.