This book is designed to help those with little or no background in the field of defect chemistry to apply its principles and to interpret the related behaviour of materials. It is the product of a course for advanced undergraduates and graduate students that the author taught at Lehigh University for over twenty years. The course is highly interdisciplinary and has been attended by students from the departments of chemical engineering, chemistry, electrical engineering, computer science, geology, materials science and engineering, and physics. The book is intended for use either as a text on such a course, or as a reference work that covers the major principles of defect chemistry.