This text on the electrical, optical, magnetic, and thermal properties of materials stresses concepts rather than mathematical formalism. Suitable for advanced undergraduates, it is intended for materials and electrical engineers who want to gain a fundamental understanding of alloys, semiconductor devices, lasers, magnetic materials, and more. The book is organized for use in a one-semester course; each section on applications, following the introduction to the fundamentals of electron theory, can be read independently of the others. Many examples from engineering practice provide an understanding of common devices and methods. Among the modern applications covered are high-temperature superconductors, optoelectronic materials, semiconductor device fabrication, xerography, magneto-optic memories, and amorphous ferromagnetics. The fourth edition has been revised.