This book has been prepared to serve as a textbook for the student of mathematics who is in the third year of an undergraduate course and also for Physics and engineering taking a first course in differential equations. The course is intended to serve as an introduction to the theory of differential equations. This book on Differential Equations consists of two parts, part one ordinary differential equation and part two partial differential equations. Part one of this book consisted of six chapters and part two of this book consisted of five chapters.