International organizations, like states, are subject to the ebb and flow of historial circumstances. They may thrive when conditions are favourable and perish when they are not. Dozens of international organizations have foundered and disappeared from the international scene since the Second World War. Some because they could not be adapted to new situations, others because of the need to rationalize international cooperation and make better use of scarce resources. In most cases, the functions and assets of the defunct international organizations were taken over by other bodies and did not devolve on the member states. Such events brought forth issues of succession between international organizations. Relatively little attention has been devoted to such problems. This is partly owing to the difficulty of gaining access to documentation and partly due to the fact that this is a rather recent phenomenon. This study approaches the subject from both a theoretical and a practical perspective. The author first establishes a conceptual framework by examining the notion of succession as it has evolved in municipal law and in the law of state succession before explaining how it applies to succession between international organizations. He then proceeds to demonstrate, through a multitude of examples taken from international practice and court decisions, the forms succession between international organizations can take, the legal basis of such succession and, finally, the effects of succession on functions, treaties, property, funds, liabilities and employees.