Since the Second World War, economists have often claimed that their discipline developed largely independently of other social sciences until it got closer to them again from the 1980s onward. Taking the story back to the end of the First World War, we show that there exists a rich history of interactions in which economists have learned from other social sciences. In the interwar period, attempts to promote interdisciplinarity were made to offset the shortcomings of too much disciplinary specialization but they concerned individual economists, notably institutionalists, more than economics as a whole. From the Second World War and in the two decades following it, the social sciences entered a cross-disciplinary age. Foundations, university administrators and scholars regarded multidisciplinary and interdisciplinary research as the key to solving social problems. Economists worked alongside mathematicians and natural scientists but they also participated in crossdisciplinary research ventures with other social scientists, an experience that often led them to depart from homo economicus and more generally from methodologies commonly taken to characterise economics. From the late 1960s, with the shift towards greater specialization, the interactions with other social scientists enjoyed less support and opportunity; they became much rarer and more individually driven, but remained significant as illustrated by the emergence and consolidation of behavioural economics.