While many scholars expect people's ideological orientations to drive their beliefs regarding the legitimacy of international organizations (IOs), research has found surprisingly limited support for this common assumption. In this article we resolve this puzzle by introducing the perceived ideological profile of IOs as a critical factor shaping the relationship between ideological orientation and such beliefs. Theoretically, we argue that citizens accord IOs greater legitimacy when they perceive these organizations as ideologically more congruent with their own orientations. Empirically, we evaluate this expectation by combining observational and experimental analyses of new survey evidence from four countries: Brazil, Germany, Indonesia, and the United States. We find that citizens indeed perceive IOs as having particular ideological profiles and that those perceptions systematically moderate the relationship between people's ideological orientations and their sense of IOs’ legitimacy. These findings suggest that political ideology is a more powerful driver of legitimacy beliefs in global governance than previously understood.