The radio emission is due to the synchrotron process. The observed structure in radio emission is determined by the interaction between twin jets and the external medium, modified by the effects of relativistic beaming. Radio galaxies are almost exclusively large elliptical galaxies. "Radio-loud" active galaxies can be detected at large distances, making them valuable tools for observation. Recently, much work has been done on the effects of these objects on the intergalactic medium, particularly in galaxy groups and clusters.