The issue of humanitarian intervention has generated one of the most heated debates in International Relations over the past decade - among both theorists and practitioners. At the heart of the debate is the alleged tension between the principle of state sovereignty, a defining pillar of the UN system and international law, and the evolving international norms related to human rights and the use of force. This edited book investigates the controversial place of humanitarian intervention in the theory and practice of International Relations. Although the subject has gained greater prominence, it continues to have an uneasy relationship with both the major schools of thought in the discipline of IR, and the behaviour of states, international organizations, and non-governmental actors. Many academic discussions focus on the question of whether there is a legal 'right' of humanitarian intervention, giving insufficient attention to the underlying ethical issues, the politics within international organizations and coalitions, and the practical dilemmas faced by international actors - before, during, and after the intervention. The book analyses humanitarian intervention through the lenses of both theory and practice, and assesses the challenges it poses for international society in a post September 11th world. It includes chapters by well-known academics from the disciplines of law, philosophy, and international relations, as well as those who have been actively engaged in cases of intervention during the past decade. The cases cover not only well-known conflicts such as Somalia and Bosnia, but also the recent international interventions in East Timor and Afghanistan. Three main themes emerge from the study. First, the contributors show that the alleged conflict between human rights and state sovereignty has been addressed by two recent developments in international society: an evolution in the notion of sovereignty from 'sovereignty as authority' to 'sovereignty as responsibility'; and an expanded definition of the Security Council on what constitutes a threat to peace and security. Second, despite this new climate of permissiveness, humanitarian intervention remains a controversial norm in International Relations, due to continued opposition from certain members of international society, and concerns about its potentially negative consequences. Finally, while the past decade has seen some successful cases of intervention to address humanitarian catastrophes, the current capability of international organizations to undertake humanitarian interventions remains limited. As the book demonstrates, the issue of humanitarian intervention has the potential to divide international institutions such as the UN and damage their credibility. This raises questions about whether and how individual members of international society should respond to humanitarian crises.