The principle of the self-determination of peoples is enshrined in the United Nations Charter and based on liberal and democratic values. However, the international community has, until recently, interpreted this principle very restrictively, so that it has amounted to little more than the right to be free from European colonialism. The collapse of the USSR and Yugoslavia, as well as persistent ethno-nationalist conflicts around the world, have provoked new thinking about the right of self-determination in political theory. This article reviews six theories, and identifies what they have in common and on what they differ. It draws some cautious policy conclusions from this analysis and, in doing so, seeks to clarify the role and limits of theory in international politics.