All optical fields undergo random fluctuations. They may be small, as in the output of many lasers, or they may be appreciably larger, as in light generated by thermal sources. The underlying theory of fluctuating optical fields is known as coherence theory. An important manifestation of the fluctuations is the phenomenon of partial polarization. Actually, coherence theory deals with considerably more than fluctuations. Unlike usual treatments, it describes optical fields in terms of observable quantities and elucidates how such quantities, for example, the spectrum of light, change as light propagates. This book is the first to provide a unified treatment of the phenomena of coherence and polarization. The unification has been made possible by very recent discoveries, largely due to the author of this book. The subjects treated in this volume are of considerable importance for graduate students and for research workers in physics and in engineering, who are concerned with optical communications, with propagation of laser beams through fibers and through the turbulent atmosphere, with optical image formation, particularly in microscopes, and with medical diagnostics, for example. Each chapter contains problems to aid self-study. Book jacket.