Jets are found in many astrophysical phenomena, from young stellar objects and collapsed stellar cores to quasar and radiogalaxies. Therefore they must represent a common dynamical phenomenon, while different morphological characteristics arise from the interaction with specific environments (Ferrari and Tsinganos 1985). In order to investigate the basic aspects of jet dynamics and morphologies, we have proposed a simple analytical treatment based on the fluid theory of stellar winds (Parker, 1063), which allows a direct test of different physical effects (Ferrari et al. 1985, 1986). We discuss here implications for the physical theories of quasars.