The third edition of this long-running Melland Schill textbook provides an accessible, up-to-date account of the principles and norms of international law as they apply to the main type of international body: the inter-governmental organisation (IGO). Concentrating on the United Nations as the paradigmatic IGO, Nigel D. White provides an account of the development of the organisation from its inception in 1945. In early chapters he discusses concepts shaped in the initial years of the UN, such as personality, powers and membership. He then goes on to consider how the legal framework has been expanded as the UN has moved into new areas, for instance in developing a range of targeted sanctions against non-state actors. Each chapter contains a number of case studies including extended analyses of non-forcible and forcible measures taken by organisations. The exercise of those powers is exposed and analysed in terms of their legality under the constituent treaty and under international laws (thereby necessitating a debate as to whether the UN is bound by international law). Finally, White considers the responsibility and accountability of the UN and similar IGOs for breaches of international law. Substantially revised from the previous edition, with a more cohesive and narrative-driven structure, this book is an essential resource for teachers and students of international organisations.