Few maps mirror the history of the twentieth century as closely as the International Map of the World (IMW). A proposal for a map of the entire globe on a scale of 1:1 million, using standard conventions and symbols, was presented at the Fifth International Geographical Congress (IGC) in Berne in 1891 by the German geographer Albrecht Penck. Over two decades later, the final specification was finally published shortly before the outbreak of World War One, a crisis that brought a halt to the international collaboration on which the project depended. The IMW’s fortunes waxed and waned over the next three decades, necessitating a major review of its continuing value after World War Two. A new IMW Executive Commission under the chairmanship of John Kirtland Wright, Director of the American Geographical Society (AGS), was established at the 1949 Lisbon conference of the International Geographical Union (IGU). Drawing on Wright’s correspondence in the AGS archives, this paper examines the debates between the national cartographic agencies and related societies involved in this project about the future of the IMW, with particular reference to the transfer of the project’s Central Bureau from the British Ordnance Survey in Southampton to the United Nations (UN) in New York in the early 1950s. This discussion, which focused mainly on the need to combine the IMW with an internationalised version of the US-dominated 1:1 million World Aeronautical Chart, reveals the on-going tensions between the ideals of scientific internationalism embodied in the IMW’s original proposal and the harsh realities of national self-interest in the early years of the Cold War.