Semiconducting and Insulating Crystals details how absorption spectroscopy provides information on the nature, concentration, charge state and configuration of impurities in crystals and also on their kinetics and transformations under annealing. After an introduction of the bulk optical properties of semiconductors and insulators and of impurities in crystals, this book presents the physical bases necessary for the understanding of impurity spectra. The description of various set-ups and accessories used in absorption spectroscopy is followed by a presentation of experimental results on specific impurities and classes of impurities and their relation with those obtained by various computation and by other experimental techniques.