This volume contains the proceedings of an AMS Special Session on Geometry, Physics, and Nonlinear PDEs, held in March 1990 at the AMS meeting in Fayetteville. In recent years, there has been an enormous surge of activity in these areas, and there was an overwhelming response to invitations to the session. The conference brought together specialists in Monge-Ampere equations, prescribed curvature problems, mean curvature, harmonic maps, evolution with curvature-dependent speed, isospectral manifolds, and general relativity. Twenty-five half-hour addresses were presented at the session, and the majority of the papers in this volume are expositions of those addresses. The book provides an excellent overview of the frontiers of research in these areas.