This book describes a variety of approaches to modelling modern semiconductor devices. The text contains a review of essential device and semiconductor physics followed by a summary of scattering processes which influence the operation of devices. Classical and semiclassical physical device models are summarized and illustrated. The application of physical device models to VLSI (silicon) devices is discussed. State-of-the-art developments in compound semiconductor devices and modelling are reviewed. The Monte Carlo modelling technique is presented, together with essential data and examples. Equivalent circuit modelling techniques are described in separate chapters for silicon (bipolar and MOS) and high frequency devices. Modelling of noise processes in semiconductor devices is discussed, together with several examples. The modelling of optoelectronic devices, - semiconductor lasers and photo-diodes, is discussed. Quantum modelling techniques and their application are presented, extending the text into the regime of ultra-small-scale devices. The book includes a summary of modern CAD software available to model devices and comments on important features in developing simulations. Lastly there is a chapter which discusses the practical aspects and applications of semiconductor device modelling.