Events such as the legal arguments surrounding the 2003 Iraq War and the creation of the International Criminal Court highlight the significance of international law in the contemporary world. This new textbook provides an introduction to the relationship between international law and international relations. David Armstrong, Theo Farrell and Hélène Lambert explore the evolution, nature and function of international law in world politics and situate international law in its historical and political context. They propose three interdisciplinary 'lenses' through which to view the role of international law in world politics: realist, liberal and constructivist. These lenses offer different ways of looking at international law in terms of what it is, how it works and how it changes. Topics covered include the use of force, human rights, international crimes, international trade and the environment, and each chapter features discussion questions and guides to further reading.