This article addresses the ways in which UNESCO’s ideological engagements are negotiated in the difference/diversity discourse as they are transferred from the international standard-setting level to the national and local contexts. It proposes the discursive construction of cosmopolitan internationalism as a framework for analysing the intersections of difference, located in the practicalities of internationalism, and diversity, tied to the ideals of cosmopolitanism, as they are manifested at the level of both the implementation of UNESCO’s Diversity Convention and urban policy making in the city of Sydney. The analysis suggests that ruptures challenging the homogenising diversity discourse rise from the national and local policy-making level, with such discourse simultaneously becoming an instrument for international differentiation. UNESCO’s normative cosmopolitan international tradition thus manifests itself as an obstacle against the emergence of transnational political spaces beyond the confines of the state, while it also carries with it a promise of facilitating such developments.