In surveying Langevin’s engagement in the World Committee Against War and FascismWorld Committee against War and Fascism and in the Comité de vigilance des intellectuels antifascistes, this chapter raises the question whether his scientific activity suffered from his commitments in the political sphere. It argues that despite his frenetic activism, Langevin maintained an intense scientific activity, even though he no longer carried out his own original research. His professional activity was divided between teaching, research training of engineers at EPCI, the management of two research units, and above all scientific consultancy through discussion with young physicists and scholars in the humanities. We argue that his career profile is typical of the French scientific establishment which favours the accumulation of functions and responsibilities among senior scientists.