Information technology has changed our society radically. Just as the integrated circuits have been the prime mover for electronics, high-speed transistors and semiconductor lasers based on heterostructures are now playing the same role in modern telecommunications. Professor Kroemer's conceptual work on heterostructures began in the early 1950s as he was looking for a way to improve transistor speed and performance. In the 1960s, he applied the same principles to the development of lasers and light-emitting diodes, showing that they could achieve continuous operation at room temperature — something thought impossible at that time. His deep fundamental scientific work has had a profound effect on technology and society, transforming and improving our lives.This reprint collection brings together Professor Kroemer's most important papers, presenting a comprehensive perspective of the field. It covers topics ranging from substrate materials, electronic properties, process technology, and devices, to circuits and applications. This reprint collection will help the reader identify the key stages in the development of heterostructure devices and lasers from early research through to its integration in current manufacturing. Devoted to R&D engineers and scientists who are actively involved in extending the nano- and microelectronics roadmap mainly via heterostructure engineering, this volume may also serve as a reference for postgraduate and research students.