The story of the origins of the post of Chief of the French Defence Staff has yet to be written, especially if we go back before 1962. It is nevertheless at the heart of the development of the French politico military system and, beyond that, of the republican model. This article gives an outline of the story, based on the few existing studies and the results of unpublished research. The whole illustrates the value of the politico-administrative approach in opening new perspectives on the history of French defence since 1870.