Research into active galactic nuclei (AGN) – the compact, luminous hearts of many galaxies – is at the forefront of modern astrophysics. Understanding these objects requires extensive knowledge in many different areas: accretion disks, the physics of dust and ionized gas, astronomical spectroscopy, star formation, and the cosmological evolution of galaxies and black holes. This new text by Hagai Netzer, a renowned astronomer and leader in the field, provides a comprehensive introduction to the theory underpinning our study of AGN and the ways that we observe them. It emphasizes the basic physics underlying AGN, the different types of active galaxies and their various components, and the complex interplay between them and other astronomical objects. Recent developments regarding the evolutionary connections between active galaxies and star-forming galaxies are explained in detail. Both graduate students and researchers will benefit from Netzer's authoritative contributions to this exciting field of research. “Professor Netzer has produced a truly impressive text on the theory and observations of active galactic nuclei. He has done a superb job of bringing both clarity and depth to what has become in recent years a very broad and complex subject. This will undoubtedly become one of the field’s defining texts and a primary resource for graduate students, their teachers, and researchers alike.” - Mark Whittle, Professor of Astronomy, University of Virginia “This volume is the most complete single treatment of active galactic nuclei in the literature, with a remarkably broad view of the relevant physical processes and data. Netzer’s text spans the intellectual range from basic theory to observational connections, better than any other treatment of AGN that I know of. This is especially important since the things we know with most assurance are observational, and the things we want to know are theoretical conclusions at various degrees of separation from the data; here one sees the whole chains of reasoning in rich detail. The text also folds in a range of recent developments, from the connections between accretion disks and outflows, through the rich statistics from recent sky surveys, to the unfolding links between AGN and their host galaxies as a normal part of galaxy evolution. This is a working reference, with useful tables and literature citations.” - William C. Keel, Professor of Astronomy and Physics, University of Alabama "… a rather splendid advanced textbook … It is authoritative and complete … if you want a single book that covers all the bases at graduate level, and gives you a jumping off point, this is the one." The Observatory A comprehensive introduction to the theory underpinning our study of active galactic nuclei and the ways we observe them. Professor Hagai Netzer is a world-class expert in the area of active galaxies and super-massive black holes. He is an associate of the Royal Astronomical Society, winner of the Humboldt and Weizmann prizes, and former director of the Wise Observatory. He has written several advanced and introductory texts in astronomy, as well as a popular science book about the search for life in the universe.