Recently there have been several examples of different regional integration systems intervening to prevent unconstitutional events. The interventions can be based on explicit powers or be developed in response to events. This happens despite most regional integration systems having economic cooperation rather than explicit democratisation aims. Organs that issue laws or take constraining decisions must have a clear right to do this and a basis for exercising power-in other words, be legitimate. Where legitimacy comes from is debated, but as most countries today are democracies or purport to be, it somehow emanates from the people. National governments have a higher degree of legitimacy than regional integration organisations, possibly except the European Union. Regional integration organisations have to prove their legitimacy. The article examines if, to what extent, and on what basis regional integration systems have the right to exercise an independent role on the global stage. Legitimacy is a precondition for effective application of decisions of the organisation. Given the frequent lack of strong enforcement mechanisms, the question of legitimacy becomes even more important. With strong legitimacy, decisions taken by the regional integration organisation will be followed to a large extent even despite absence of effective enforcement mechanisms.