Novel microelectronic and optoelectronic devices are based on semiconductor heterostructures. The present book discusses various questions related to the use of new materials, such as compound semiconductors based on high band-gap nitrides and low band-gap antimonides, and new procedures, such as low-temperature epitaxial growth, and new principles, such as nanostructures, quantum wires and dots, the aim being to achieve high-performance heterostructural electronic devices.