Quasars and active galaxies are the most powerful emitters of radiation in the universe. Modern radio telescope arrays have shown that the ultimate energy source resides in the central few parsecs of the galactic nucleus, and powers the emitting regions by way of two oppositely-directed relativistic jets of energy. This volume presents the latest observations and theories of these remarkable objects. Topics discussed include superluminal motions, the physics of jets and shock fronts in jets, related optical observations, and cosmic evolution. Particular attention is given to the unified theories, which attempt to show that many of the phenomena in powerful extragalactic objects are different aspects of a single, basic mechanism; the main difference in their appearance is a result of their different orientation with respect to the observer.