Most stars appear to show some degree of magnetic activity. For example, the varying magnetic field of the Sun shows up in the familiar sun-spot cycle. Radio and X-ray pulsars are enormously dense, rapidly rotating neutron stars which carry steady magnetic fields that are far stronger than the average magnetic field of the Sun. Likewise, many uncollapsed stars behave like rotating permanent magnets. Furthermore, magnetic fields may partly control the formation of new stars as well as the spectacular behaviour observed in galactic nuclei.Stellar magnetism is therefore a rapidly develoing field of astrophysics, and this book has grown out of the lifelong work of an outstanding researcher in the area. It is an authoritative account with broad astronomical scope, and its thorough, careful, and well-argued approach make it a fine addition to the professional literature. Most of the important topics are treated in mathematical depth with reference given to other relevant literature. Some of the studies, especially those on accretion discs, dynamos, and winds, are applicable to galaxies and galactic nuclei. As well as acting as a professional reference and guide to current thinking, this book will be of interest to graduate students, for whom it shows how the subject has developed and leads on to research problems in the field.