Public International Law

States often need to cooperate with each another to address legal and other issues of common concern across many fields in an interdependent world. International organisations (‘IOs’) emerged in the 19th century as a means of intensifying and permanently institutionalising international cooperation, through bodies with an international legal personality, and functions and powers, separate from their member states. While the earliest IOs had a narrow technical focus, the League of Nations (1919–46) and United Nations (since 1945) reflect a more ambitious global agenda of broad-spectrum cooperation. The proliferation of IOs has generated some key legal issues which this chapter explores: how to define IOs; the nature, extent and consequences of their international legal personality; their powers, immunities and privileges; and the scope of their legal responsibility for their conduct. There is a special focus on the United Nations, as a universal IO with competence in many areas of international life and human activity, and from whose establishment and practice much of the international law of IOs has emerged.