  The history of Weyl’s discovery is quite unlike the history of Lie  groups and Grassmann algebras. Weyl was neither obscure nor  unrecognized, and he was working in 1918 in the most fashionable area of physics, the newborn theory of general relativity. He invented  gauge fields as a solution of the fashionable problem of unifying  gravitation with electromagnetism. For a few months gauge fields were at the height of fashion. Then it was discovered by Weyl and others  that they did not do what was expected of them. Gauge fields were in  fact no good for the purpose for which Weyl invented them. They  quickly became unfashionable and were almost forgotten. But then,  very gradually over the next fifty years, it became clear that gauge  fields were important in a quite different context, in the theory of  quantum electrodynamics and its extensions leading up to the recent  development of quantum chromodynamics. The decisive step in the  rehabilitation of gauge fields was taken by our Princeton colleague  Frank Yang and his student Bob Mills in 1954, one year before Hermann Weyl’s death [Yang and Mills, 1954]. There is no evidence that Weyl  ever knew or cared what Yang and Mills had done with his brain-child. 