Robert Triffin (1911-1993) played an important role in the international monetary debates in the postwar period. He was known as one of the main advocates of a multipolar international monetary system. In this paper we analyse the origins of Triffin’s “regional” approach towards international monetary integration. We argue that Triffin’s experience with the European Payments Union (EPU) played hereby a crucial role. Triffin was not only an “architect” of the EPU, but the EPU also led to an important shift in Triffin’s view of the geography of the international monetary system. Before his work on the EPU, Triffin thought of the international economy as composed of two geographical entities: national economies and the world economy. With his work on the EPU he introduced a third geographical entity: the region. The EPU would so be at the basis of Triffin’s advocacy of a regional approach towards international monetary integration. Moreover, while Triffin was initially quite positive on the IMF, he became, through his EPU experience, more critical of the IMF and its worldwide approach.