Despite the long history of the semiconductor laser, it remains a subject of active research. New scientific tasks require better performance and novel functionalities of light sources, while new achievements in semiconductor lasers expand the area of their possible applications. For these reasons, an up-to-date summary of their science and technology is highly desirable, which is the purpose of this book. The introductory section discusses the fundamentals of semiconductor lasers. It begins with a chapter presenting their general principles, then moves on to explore photonic crystal lasers, the development of high power lasers, laser arrays, and the generation of ultrafast light pulses by semiconductor lasers. Part two is devoted to semiconductor lasers that are well suited for operation in the visible and near infrared spectral regions. Chapters summarize the latest achievements in the field of short wavelength semicondutor lasers based on nonpolar and semipolar GaN and its alloys, review quantum dot lasers, analyze electrically and optically pumped vertical cavity surface emitting lasers, and discuss hybrid integration of III-V lasers on silicon. The third, and final, section describes several other types of semiconductor lasers operating in the mid- and far-infrared, such as GaSb-based type I quantum well diode lasers, interband cascade and terahertz quantum cascade lasers, whispering gallery mode lasers, and tunable mid-infrared laser absorption spectroscopy.