In the Second World War, the Allies waged war on a truly global scale for the first and, one hopes, last time in history. Victory required the mobilisation and transportation of wo/men and materiel on all continents and across four out of the Earth’s five oceans. Success would have been impossible without extensive inter-Allied coordination, organisation and planning. Starting in 1939, a system of inter-Allied organs was set up by Britain and France, whose mission it was to coordinate the supply of the Allied war effort from a common pool. It survived France’s fall in 1940 and, upon US entry in 1941, was revived. By 1942, it had evolved into a global network of military, production and logistics experts from India to Canada and South Africa to Norway, organised into a series of so-called Combined Boards and dedicated to the nuts and bolts of worldwide coalition warfare. Yet we lack a history of this extraordinary organisation. Despite the Second World War’s self-evidently global nature, the tendency to frame it in national, comparative and Eurocentric terms is very deeply entrenched. INTERALLIED, by contrast, seeks to highlight the global, transnational and interdependent character of the Allied war effort. The project asks: how did the Allies seek to couple, then uncouple their war economies, and mobilise (then demobilise) global markets for war, between 1939 and 1945? It seeks (1) to provide an account of the political economy of global Allied warfare, and thus to reach for a history of the global economy at war, which has yet to be written; (2) to advance a recent 'global turn' in Second World War studies, and thus to resist nationalistic and Eurocentric readings of the conflict, frequently deployed politically today; and (3) to produce new, practical knowledge about how societies can cope with massive shocks to their systems of supply, production and trade, and prevent damaging and wasteful competition for scarce resources.