Following the downfall of fascism in World War II, the old alliance of modernism and socialism dispersed, as architecture was sucked into the confrontation of the Cold War. In response, a new type of international architectural organisation emerged, shaped not by utopian idealism but by cultural diplomacy and international goodwill, along with consensual policy objectives, such as advancement of the architect's professional status. The most influential international organisation of architects — the ‘United Nations’ of architecture — was the Union Internationale des Architectes/International Union of Architects (UIA/IUA), a Paris-based society headed by the Hungarian-born Pierre Vago. Although only a small organisation, like many NGOs in symbolic areas of cultural activity, the UIA exploited the polarisations of the Cold War, carving out an influential mediating niche for itself. This paper focuses on the UIA congresses during the period of greatest Cold War instability — Moscow, 1958; London, 1961; Havana/Mexico City, 1963 — showing how the first and third projected the Union into hotbeds of Cold War instability.