More than any other activity, the Solvay CouncilsSolvay Council on the international stage demonstrated Langevin’s scientific style. His excellence was attributed to a “quite broad, quick and lucid intelligence” that qualified him to guide the developments of physics during his mission as chairman of the international scientific committee. The minutes of the meetings suggest that he did not impress his colleagues by sharp criticisms, as Einstein did. Instead, he adopted a low profile but he was qualified to synthesize the debates on all topics. When he chaired the debates in the 1930s he tried to play the role of a neutral referee although he clearly sided with Einstein. A direct result of Langevin’s participation in the physics councils between 1911 and 1939 was the invisible, counted and uncounted friendships, with Einstein in particular.