This is a useful textbook for graduate students in the fields of solid state physics and chemistry as well as electronic engineering. Presenting the fundamentals of amorphous semiconductors clearly, it will be essential reading for young scientists intending to develop new preparation techniques for more ideal amorphous semiconductors e.g. a-Si:H, to fabricate stable and efficient solar cells and thin film transistors and new artificial amorphous materials such as multilayers for quantum devices.A large portion is devoted to the latest developments of amorphous semiconductors including electronic properties of a-Si:H, nature of weak bonds and gap states in a-Si:H, mechanisms for light-induced defect creation in a-Si:H and chalcogenides, quantum phenomena in multilayer films.