Enlarged and updated in 1983, this is the second edition of Dr Steel's popular textbook on interferometry. The text has been revised throughout and major additions have been made to reflect the phenomenal growth of laser techniques and applications. The book provides a general treatment that brings together the many different applications of the interference of light waves, light being used in its most general sense to include all electromagnetic radiation. The applications can cover precise measurement of length, the testing of optical components against a computed hologram, measurements of atmospheric pollution by infrared spectroscopy and many of the methods of radio astronomy and the measurement of size of visible stars. These apparently unrelated methods have a common theory, which the book presents and extends to each main field of application. It shows workers in one field how their problems relate to those in other fields, where they may have been solved already. The book will be found useful by anyone whose work involves one of the many applications of interferometric techniques.