This textbook links characteristic features of atomic and electronic structures of disordered semiconductors to the device design process. It begins with a description of general concepts of disordered semiconductors, their atomic structures, the structure of energy bands, and their defects, as well as their electrical, optical, and photovoltaic properties. Since weak sensitivity to impurities is a distinguishing feature of disordered semiconductors, methods of property control and thin-film preparation methods are the areas of focus. Finally, applications of disordered semiconductors in various devices are considered.