2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/4184Observations of warm absorbers provided new ways to study the nuclear environments of AGNs. I discuss basic properties of warm absorbers and early developments with ROSAT, ASCA and HST observations. I briefly touch upon recent advances made with Chandra and FUSE.Invited review presented at the "Multicolour Universe" conference, held in Mumbai, India, Sept. 2001Astrophysicstext