This book is intended to give an introduction to the field of partial differential equations. The presentation is intentionally not too brief so that graduate students should be able to read it without serious difficulty. In addition to requiring a thorough knowledge of differential and integral calculus as well as of the theory of ordinary differential equations, it presupposes a few results from complex variables, and, in its last part, a few from func tional analysis and real variables. The goals of the book necessitated a careful selection of material. Of course, in the framework of this...