[en] One of the characteristics of modern science and technology is the extraordinary overlapping pattern of the contributions by different teams working on the same problem in different countries. As a result, it is difficult, and sometimes even presumptuous, to endeavour to remove from its international context and single out the contribution made to a common problem by one particular team. I shall nevertheless attempt here to describe the part played by French scientists in the series of developments that led to the epoch-making start-up of Fermi's reactor in Chicago on 2 December 1942, the event that was the genesis of the atomic problem, on the evolution of which the fate of our civilization depends. (author)