  The basic ideas and the important role of gauge principles in modern
elementary particle physics are outlined. There are three theoretically
consistent gauge principles in quantum field theory: the spin-1 gauge principle
of electromagnetism and the standard model, the spin-2 gauge principle of
general relativity, and the spin-3/2 gauge principle of supergravity. (Dirac
Prize lecture, November 1993. Two figures are unavailable, but should not be
essential.)
