A brief overview of models of jet formation from accretion disks orbiting black holes in active galactic nuclei and Galactic X-ray binary stars as well as from young stellar objects is presented. A strong case can now be made that accretion and jet formation are controlled by hydromagnetic forces. However, the observations indicate that there are various modes of accretion and have reinvigorated the study of large scale MHD, dissipation mechanisms, particle acceleration and radiation processes. Future prospects are bright. ©1998 American Institute of Physics.