  The theory of gamma-ray emission from e$^{\pm}$ jets and the implications for
jet formation, dynamics and structure are reviewed. In particular, possible
carriers of the jet's thrust on small scales, the transition from
electromagnetic to particle dominance in Poynting flux jets, formation of pair
cascades, synchrotron emission by cascading pairs, and formation of shocks due
to unsteadiness in the jet parameters are considered, with emphasis on the
observational consequences. Some recent progress in modeling transient emission
from blazars is also briefly discussed.
