This outstanding collection of surveys addresses graduate and predoctoral students. It reports on theoretical research and observational data on active galactic nuclei: The enigma of the nuclei of galaxies with their central "monster" driving the vast range of activity observed in quasars, radio galaxies, Seyferts, starburst galaxies and even our own Galaxy are explored in this volume. Topics covered include: the impact of recent measurements in the infrared and radio region on our knowledge of thenucleus of our Galaxy; the spectra and classification of active galactic nuclei, the properties...