  The nuclei of most normal galaxies contain supermassive black holes, which
can accrete gas through a disk and become active. These Active Galactic Nuclei,
AGN, can form jets which are observed on scales from AU to Mpc and from meter
wavelengths to TeV gamma ray energies. High resolution radio imaging and
multi-wavelength/messenger campaigns are elucidating the conditions under which
this happens. Evidence is presented that: AGN jets are formed when the black
hole spins and the accretion disk is strongly magnetized, perhaps on account of
gas accretingat high latitude beyond the black hole sphere of influence; AGN
jets are collimated close to the black hole by magnetic stress associated with
a disk wind; higher power jets can emerge from their galactic nuclei in a
relativistic, supersonic and proton-dominated state and they terminate in
strong, hot spot shocks; lower power jets are degraded to buoyant plumes and
bubbles; jets may accelerate protons to EeV energies which contribute to the
cosmic ray spectrum and which may initiate pair cascades that can efficiently
radiate synchrotron gamma rays; jets were far more common when the universe was
a few billion years old and black holes and massive galaxies were growing
rapidly; jets can have a major influence on their environments, stimulating and
limiting the growth of galaxies. The observational prospects for securing our
understanding of AGN jets are bright.
