The book contains the contributions to the conference on "Partial Differential Equations" held in Holzhau (Germany) in July 1994, where outstanding specialists from analysis, geometry and mathematical physics reviewed recent progress and new interactions in these areas. Topics of special interest at the conference and which now form the core of this volume are hyperbolic operators, spectral theory for elliptic operators, eta-invariant, singular configura- tions and asymptotics, Bergman-kernel, attractors of non-autonomous evolution equations, pseudo-differential boundary value problems, Mellin pseudo- differential operators, approximation and stability problems for elliptic operators, and operator determinants. In spectral theory adiabatic and semiclassical limits, Dirichlet decoupling and domain perturbations, capacity of obstacles, limiting absorption problems, N-body scattering, and number of bound states are considered. Schrödinger operators are studied with magnetic fields, with random and with many-body potentials, and for nonlinear problems. In semigroup theory the Feller property, errors for product formulas, fractional powers of generators, and functional integration for relativistic semigroups are analyzed.