  Most models for blazars and gamma-ray bursts involve relativistic plasma
outflows powered by accretion processes onto black holes. The blast wave
physics developed for cosmological models of GRBs is reviewed. Two points
relevant for blazar modeling are made: (1) The injection of nonthermal
relativistic particles in the comoving frame is simply treated though a process
of energizing the plasma as it sweeps up material from the surrounding medium.
(2) The primary energy source of blazar radiation derives from the bulk kinetic
energy of the outflowing plasma. Thus deceleration of the plasma blast wave
must be included in blazar flaring calculations, and this process will
introduce temporal and spectral effects in addition to those produced by
acceleration and radiative cooling.
