This textbook is an elementary introduction to the basic principles of partial differential equations With many illustrations it introduces PDEs on an elementary level enabling the reader to understand what partial differential equations are where they come from and how they can be solved The intention is that the reader understands the basic principles which are valid for particular types of PDEs and to acquire some classical methods to solve them thus the authors restrict their considerations to fundamental types of equations and basic methods Only basic facts from calculus and linear ordinary differential equations of first and second order are needed as a prerequisite The book is addressed to students who intend to specialize in mathematics as well as to students of physics engineering and economics Second revised and extended edition Examples with real world problems With many illustrations