The existence of jets emanating from the central sources of radio galaxies and quasars was an important discovery for our understanding of the nature of active galactic nuclei. This volume presents reviews and research papers on extragalactic radio sources. It begins with a discussion of the phenomenology and models of radio sources. The main part is devoted to detailed studies of jets by VLBI, to the information obtained about the structure of the central source as deduced from variability studies, to the production, confinement and velocity of jets as well as to numerical simulations of the jet phenomenon. Reviews of the two best-studied jets - those in the radio galaxy M87 and the quasar 3C273 - illustrate our current observational picture of extragalactic radio jets in all accessible wavelength ranges. A section on the influence of the environment on radio galaxies concludes the book.