This article examines how the International Labour Office (ILO) tried to disseminate one of its statistical tools, the International Standard Classification of Occupations (ISCO), in sub-Saharan Africa, in the context of decolonization and development planning. It sheds light on the changing relations in the late 1950s and early 1960s between the ILO, late colonial and then national administrations, and a regional organization, the Combined Commission for Technical Cooperation in Africa South of the Sahara (CCTA). Although characterized by rivalry, misunderstandings, and sometimes indifference, these relations were also marked by partially overlapping interests. Focusing on the successive ILO experts responsible for developing occupational classifications, this paper shows how their interactions with local actors reshaped the project which they had to carry out. For instance, it gave a greater place to the training of national civil servants or contributed to the realization of the 1962 Nigerian census. In particular, the article analyzes the connections made with other international programs (relating to demography and economic planning) on the ground, and the resulting interdependence among them. By doing so, the ILO expert responsible for the project on occupational classifications benefited from the resources of other technical assistance programs and tried to demonstrate to national authorities the importance of the project which could apply in various fields. While unexpected difficulties limited the scope of the initial project to Nigeria alone, the paper discusses how ILO officials inscribed occupational classifications in the general framework of development planning.