Elites are central in creating, operating, defending and contesting international organisations (IOs), but little research is available about their attitudes toward these bodies. To address this gap, this article offers the first systematic and comparative analysis of elite perceptions of IO legitimacy. Building on a unique multi-country and multi-sector survey of 860 elites undertaken in 2017-19, we map and explain elite legitimacy beliefs toward three key IOs in different issue-areas: the International Monetary Fund (IMF), the United Nations Framework Convention on Climate Change (UNFCCC) and the United Nations Security Council (UNSC). Integrating public opinion research and international relations theory, the article advances an explanation of elites' legitimacy beliefs that emphasises their satisfaction with the institutional qualities of IOs. We contrast this argument with three common alternative explanations, which respectively highlight utilitarian calculation, global orientation and domestic cues. The analyses show that elites' satisfaction with institutional qualities of IOs is most consistently related to legitimacy beliefs: when elites are more satisfied with democracy, effectiveness and fairness in IOs, they also regard these IOs as more legitimate. These findings suggest that the prevailing debate between utilitarian calculation, global orientation and domestic cues approaches neglects the importance of institutional satisfaction as an explanation of attitudes toward IOs.