The new Astronomers' Universe Series is aimed at the same readership as the Practical Astronomy Series - active amateur astronomers. This book provides an up-to-date account of active galaxies which are a major field of current astronomical research - up to a fifth of all research astronomers are working on active galaxies. Lists of such objects and their visual and imaged appearance in commercially available telescopes are an important component of this book. This is the first coherent and complete source of information for non-technical readers on an area of astronomy that fascinates many people. It makes sense of the chaotic and apparently innumerable types of violently active galaxies. It also provides the data and teaches the skills needed for users of small telescopes to observe and image some of these "galaxies in turmoil" for themselves.