These lectures stress the fundamental ideas relevant to understanding the electrical properties of materials. Topics have been selected to explain the operation of devices that have direct application in the field of engineering, and the text is kept at a level comprehensible to second-year engineering students. Over the past few years there have been remarkable advances in the technology of semiconductor and laser devices. Revised and updated to include these new developments, the book covers the field of superconductivity and contains a completely new chapter on optoelectronics. The chapter on lasers has been rewritten and new problems and examples have been added throughout the text. The book thus serves as an informative, up-to-date reference for students in electrical engineering and physical electronics as well as for practicing engineers.