2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/3999A review of the spectroscopic tools needed to characterize AGNs is presented. This review focusses on ultraviolet, optical and infrared emission-line diagnostics specifically designed to help differentiate AGNs from starburst-dominated galaxies. The strengths and weaknesses of these methods are discussed in the context of on-going and future AGN surveys.Invited review, to appear in the proceedings of IAU Colloquium #184 "AGN Surveys" held at the Byurakan Observatory, Armenia in June 2001 (15 pages including 6 figures, LateX, newpasp.sty macro)Astrophysicstext