War is invariably accompanied by debate, if not controversy, over the legitimacy of using force. Alongside the longstanding state practice of justifying use of force is the increasing codification of legal rules on the use of force. In this volume a leading group of international authorities consider the issues surrounding the legitimation of force from several distinct disciplinary perspectives, including political science, law, history and philosophy. In particular, they examine the underlying question of whether and how international society's traditional norms of sovereignty and non-intervention can coexist both with the new norm of humanitarian intervention and with an increasingly hegemonial (if not 'imperial') role played by the United States. What is the difference between 'legality' and 'legitimacy'? Is the latter a truly universal concept or mainly a Western one? Are earlier ideas about 'just war' still relevant?

David Armstrong is Professor of International Relations, Department of Politics, University of Exeter. Theo Farrell is Reader in War in the Modern World, Department of War Studies, King's College London. Bice Maiguashca is Lecturer in Politics, Department of Politics, University of Exeter.