2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/7937The formation of powerful extragalactic jets is not well understood at present as well as the associated key question:``What makes an AGN radio loud?''. Here we discuss how the combination of VLBI and X-ray spectroscopic observations allows the inter-relation between the accretion flow and the formation of relativistic jets in AGN to be explored.2 pages, 1 figure, Proceedings of the conference "Exploring the Cosmic Frontier - Astrophysical Instruments for the 21st Century" held at Berlin in May 2004, to be published in the Springer-Verlag series "ESO Astrophysics Symposia", needs physprbb.sty and svmult.clsAstrophysicstext