"Version: 202112"--Title page verso.Includes bibliographical references.1. Introduction -- 1.1. Some brief history -- 1.2. Excitation of lines, masses -- 1.3. Variability and size -- 1.4. Global spectrum SED -- 1.5. The central engine -- 1.6. The AGN zoo, blazars, quasars, and others -- 1.7. Emission lines, and the BPT diagnostics -- 1.8. Unification models -- 1.9. Radio galaxies, and radio pro…