This book contains the first unified account of the currently used mathematical models for charge transport in semiconductor devices. It is focussed on a presentation of a hierarchy of models ranging from kinetic quantum transport equations to the classical drift diffusion equations. Particular emphasis is given to the derivation of the models, an analysis of the solution structure, and an explanation of the most important devices. The relations between the different models and the physical assumptions needed for their respective validity are clarified. The book addresses applied mathematicians, electrical engineers and solid-state physicists. It is accessible to graduate students in each of the three fields, since mathematical details are replaced by references to the literature to a large extent. It provides a reference text for researchers in the field as well as a text for graduate courses and seminars.