This book provides the theoretical basis and the relevant experimental knowledge underlying our present understanding of the electrical and optical properties of semiconductor heterostructures. Although such structures have been known since the 1940s, it was only in the 1980s that they moved to the forefront of research, largely due to technological developments that made it possible to grow several ultrathin layers of different materials _ down to a few atoms in thickness _ on top of a silicon or other substrates. The resulting structures have remarkable properties not shared by bulk materials. One can, for example, confine the motions of electrons to a single layer, making it possible to investigate effectively two-dimensional systems. One can also build materials with large-scale periodicities by alternating layers of different compositions, thereby modulating the optical and electronic properties of the resulting structure. The text begins with a description of the electronic properties of various types of heterostructures, including discussions of complex band-structure effects, localized states, tunneling phenomena, and excitonic states. The focus of most of the remainder of the book is on optical properties, including intraband absorption, luminescence and recombination, Raman scattering, subband optical transitions, nonlinear effects, and ultrafast optical phenomena. The concluding chapter presents an overview of some of the applications that make use of the physics discussed. Appendices provide ackground information on band structure theoy, kinetic theory, electromagnetic modes, and Coulomb effects. Intended for graduate students, physicists, and engineers beginning research on semiconductor heterostructures or interested in their