During the second half of the 20th century, at the time of the foundation of the Fifth Republic, French engineers endorsed enthusiastically technocratic ideals. Their attitude was not only the product of a specific context. It was rooted in a long tradition of connection between French engineering and social preoccupations. This connection emerged at the time of the creation of the first corps of State engineers in the 17th and 18th centuries. Indeed, State Weber engineers were from the start convinced that they had a social mission. Subsequent episodes, like the Saint-Simonian reflections on the eve of industrialization, or the discussions held in the think tank X-Crise in the aftermath of the 1929 economic crisis contributed also to shape the engineers' sensitivity to social issues. Dwelling on these episodes, but also trying to go beyond their standard assessment, we would like to propose here a more general interpretation of the complex set of relations between French engineering and social thought. In this perspective, the Post-World War II French engineers' technocratic concerns come at the end of a long and complex evolution. This case study should enable a better understanding of the more general connivance between engineering culture and technocratic ideals.