This book explains the basic elements that readers need to know about amorphous silicon material and a-Si:H TFTs. It includes the main principles of the transistors operation, modeling and applications. Fundamentals about transport mechanisms in a-Si:H TFTs and the associated electronic properties are introduced and extended to design examples and strategies to build reliable, large-area, performance optimized circuits. The book also reviews the effect of the amorphous silicon nature and how it impacts the transistors properties and their relevant applications. Fundamentals are made as simple as possible to be easily grasped as they cover everything expected to be important for an easy understanding of the introduced concepts. The author's approach is geared toward undergraduate and graduate students, but the content is also appropriate for circuit simulator developers, integrated circuit designers and manufacturers, as well as everyone engaged in work on large area integrated circuit technologies and photovoltaics.