This volume provides a full account of the many exciting recent advances in both observational and theoretical research on sunspots and is intended to serve as a monograph on the subject. It contains eighteen authoritative review articles on various aspects of the physics of sunspots, each of which is an expanded version of an invited review paper presented at the NATO ARW on the Theory of Sunspots in 1991. Chapters on starspots and on the relation between sunspots and the global-solar-magnetic field and the solar cycle place the subject in a broader astrophysical context. An extensive introductory chapter by the editors presents an overall view of modern research on sunspots from a historical perspective, with a comprehensive list of references, and makes this book suitable for students and nonspecialists, as well as the sophisticated reader.