The book contains a unified approach to crystallography and structural imperfections and defects found within crystals. Split in two parts, this volume combines the classical and exact description of symmetry of a perfect crystal with the possible geometries of the major defects_dislocations, stacking faults, point, surface, and volume defects, twins, and the effects of martensitic transformation in iron. It presents a large amount of the latest critically evaluated data for the properties of all elements on the periodic table, including hundreds of up_to_date crystal structure data. Strongly supporting learning, each chapter contains suitable chosen examples and worked problems to absorb concepts and topics faster. The book was primarily intended as an undergraduate or graduate level textbook for students in both materials science and mechanical engineering meeting the topic of materials structure for the first time, but also would be helpful to scientists and educators who desire supplementary information.