How was ‘international trade’ between former European empires and their former colonies in Africa governed after decolonisation? In the 1960s, the vast majority of African countries became independent, and so a new arrangement was necessary to govern their economic relations with Europe. The Yaoundé Conventions were then concluded between the European Community (EC) and the bloc of postcolonial African countries. Specialised literature provides comprehensive accounts of the Yaoundé Conventions. However, little is known about the role of law and lawyers in their making and governance. Part of this story concerns political and intellectual struggles in the legal profession about which projects, ideas, and norms would be applicable. Another part concerns the work of lawyers to organise those policies, theories and visions into an emerging conception and to employ it to influence the production and management of the Yaoundé Conventions. This article combines historical and socio-legal approaches to show that a distinct legal conception of regional trade agreements—called here the ‘development framework’—was pivotal to the design and application of the Yaoundé Conventions. This conception was primarily advanced and persuasively used by European and African lawyers. This contrasts with the conventional view that trade agreements are variations on a single legal concept. It is concluded that EC–Africa regionalism was a singular experiment, due significantly to the unique features of this legal conception.