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. 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.