2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/15376Results from recent multiwavelength observations of blazars are reviewed, with particular emphasis on those involving the Rossi X-ray Timing Explorer (RXTE). I discuss blazars' spectral energy distributions, their correlated variability at various energies, and the insights they offer on the physical processes in the jet. New results on Mrk 501, PKS 2155--304, and PKS 2005--489 are highlighted.invited review talk at the Frascati Workshop 1999, May 24-29 1999, Vulcano, Italy, MEMSAIt, in pressAstrophysicstext