Active galactic nuclei (AGN) are among the most spectacular objects known to astronomy. Yet, despite years of intense and wide-ranging research, the debate over their fundamental source of power continues. In this volume, the contributors address such topics as what evidence there is for and against unified schemes for AGN and how the AGN populations evolve over cosmological timescales. Rapid progress has been made toward answering some of these questions by a variety of large-scale, multi-wavelength monitoring campaigns and the latest generation of satellite-borne observations. This volume provides a valuable overview and timely update of the exciting and rapidly developing field of AGN research for students and researchers in the fields of astronomy and astrophysics.