This textbook explains the basic principles that readers need to know about amorphous silicon material and a-Si based transistors. The author’s approach is geared toward undergraduate and graduate students, but the content is also appropriate for circuit simulators developers, integrated circuits designers and manufacturers, as well as everyone engaged in work on large area integrated circuits (ICs) technologies and photovoltaics. Fundamentals are made as simple as possible, to be easily grasped and the book includes the main principles of the a-Si:H TFTs operation, modeling and applications. The author also includes design examples and strategies to build reliable, large-area, performance optimized circuits.