Legitimacy is commonly cited as one of three fundamental mechanisms of social control within both domestic politics and international society. However, despite growing attention to the legitimacy of global governance, little consideration has been given to the identity of the political communities that must grant legitimacy to an international organisation or to the conditions under which legitimacy is valuable for the functioning of that organisation. In raising and responding to these questions, this article rejects the argument that actors must gain legitimacy among all subject social constituencies within their political realm of action. Instead, the importance of legitimacy within a particular constituency is a variable. The article labels this variable a legitimacy nexus and outlines five factors that are hypothesised to contribute to calibrating a legitimacy nexus. The plausibility of the proposed schema is explored through discussion of the role of legitimacy in the trade regime and analysis of the origins of the International Labour Organization's anomalous tripartite representative structure.