This article examines Allied peace planning during the latter stages of the First World War by comparing and connecting the British, French, and American expert groups. These academic experts were expected to apply the publicly announced programme of national self-determination to the local realities in Europe without losing sight of their governments’ geopolitical directives. Contacts and exchanges between the three groups, largely neglected in the literature, played a crucial role in shaping the experts’ work. At the same time, persisting national suspicion and the fragile institutional position of the experts prevented open debate on the precise meaning of national self-determination and thereby forestalled the development of a coherent Allied peace programme. This shortcoming would become a serious burden for the negotiations at the Paris Peace Conference and the early interwar period, in that it led to growing frustration and undermined Allied commitment to the Paris peace treaties.