Late in October 1911, eighteen leading scientists from all over Europe met to the first of a famous sequence of Solvay conferences in Brussels. This historical meeting was mainly devoted to "The Theory of Radiation and the Quanta", at a time when the foundations of physics were totally shaken. Although "nothing positive came out" (Einstein), it is interesting to see the diverging attitudes of Europe's most famous scientists in the middle of the quantum revolution. After a few general remarks about the conference, I shall focus on some of the most interesting contributions and discussions. Einstein, at 32 the youngest, was clearly most aware of the profound nature of the crises. He gave the final talk entitled "The Present State of the Problem of Specific Heats", but he put his theme into the larger context of the quantum problem, and caused a barrage of challenges, in particular from Lorentz, Planck, Poincaré, and others.