Infrared astronomy has been revolutionised in the last few years by the advent of large, sensitive, infrared arrays, and the success of several infrared satellites. This handbook provides a clear, concise and accessible reference on all aspects of infrared astronomy. Throughout, the emphasis is on fundamental concepts, practical considerations and useful data. Starting with a review of the basic infrared emission mechanisms, we are shown how the earth's atmosphere affects and limits observations from ground-based telescopes. The important systematics of photometric accuracy are treated in detail. Spectroscopy - both stellar and otherwise - is explained, and illustrated with useful examples. An important chapter is devoted to dust, which plays such a central role. Finally, the technical background to infrared instrumentation is covered. This volume provides both an essential introduction for graduate students making infrared observations or reducing infrared data for the first time, and a convenient reference for more experienced researchers.