Abstract Recent advances in the science and technology of Si/SiGe heterostructures and devices based on them are reviewed. The crystal growth techniques used to prepare these heterostructures, the material properties and band structure are discussed. Transport and optical properties of the Si/SiGe system modified by strain are treated. This is followed by a discussion of quantum wells and superlattices, and their applications to electronic and optical devices. Among the devices covered are heterounction bipolar transistors, field effect transistors, near- and far-IR photodetectors, and light-emitting devices.