Jets in active galactic nuclei are created in accretion disks around supermassive black holes, and they can retain their collimation up to the order of a megaparsec. To understand the physical causes of this remarkable collimation over such large distances is a great challenge and could lead to important new insights in the physics of magnetoplasmas. In the present work we take a two- pronged approach. First, we simulate the behavior of jets using a new, recently developed, mathematical model. Second, we analyze the observational evidence from the well- defined jet of the relatively distant radio galaxy 3C 303. We derive new constraints on the plasma properties of the jet. The final goal is to determine the ability of MHD models to describe the collimation of extragalactic jets, their physical nature, and their role in formation of radio lobes.