This volume contains the contributions of participants of the conference "Optimal Control of Partial Differential Equations" held at the Wasserschloss Klaffenbach near Chemnitz (Saxony, Germany) from April 20 to 25, 1998. The conference was organized by the editors of this volume. Along with the dramatic increase in computer power, the application of PDE-based control theory and the corresponding numerical algorithms to industrial problems has become more and more important in recent years. This development is reflected by the fact that researchers focus their interest on challenging problems such as the study of controlled fluid-structure interactions, flexible structures, noise reduction, smart materials, the optimal design of shapes and material properties and specific industrial processes. All of these applications involve the analytical and numerical treatment of nonlinear partial differential equations with nonhomogeneous boundary or transmission conditions along with some cost criteria to be minimized. The mathematical framework contains modelling and analysis of such systems as well as the numerical analysis and implemention of algorithms in order to solve concrete problems. This volume offers a wide spectrum of aspects of the discipline and is of interest to mathematicians as well as to scientists working in the fields of applications.