Semiconductor optoelectronic devices are at the heart of all information generation and processing systems and are likely to be essential components of future optical computers. With more emphasis on optoelectronics and photonics in graduate programmes in physics and engineering, there is a need for a text providing a basic understanding of the important physical phenomena involved. Such a training is necessary for the design, optimization, and search for new materials, devices, and application areas. This book provides a simple quantum mechanical theory of important optical processes, i.e. band-to-band, intersubband, and excitonic absorption and recombination in bulk, quantum wells, wires, dots, superlattices, and strained layers including electro-optic effects. The classical theory of absorption, quantization of radiation, and band picture based on k p perturbation has been included to provide the necessary background. Prerequisites for the book are a knowledge of quantum mechanics and solid state theory. Problems have been set at the end of each chapter, some of which may guide the reader to study processes not covered in the book. The application areas of the phenomena are also indicated.