Magnetic activity in the sun and similar stars results in a wealth of phenomena — including starspots, nonradiatively heated outer atmospheres, activity cycles, deceleration of rotation rates, and even, in close binaries, stellar cannibalism. This volume uniquely combines studies of the sun with those of other stars to provide a comprehensive picture of stellar magnetic activity. Coverage brings together recent results in solar and stellar studies to provide an illuminating, new view of the subject. Key topics include radiative transfer, convective simulations, dynamo theory, outer-atmospheric heating, stellar winds and angular momentum loss. Researchers are provided with a state-of-the-art review of this exciting field. Graduate students in astrophysics and plasma physics will find the volume an ideal introduction to the subject. The book will also interest researchers studying the connection of solar Sctivity with the Earth's climate change, such as geologists, planetary scientists and atmospheric scientists.