  The discovery of strong gamma-ray and hard X-ray emission and the results
from various multifrequency campaigns have disclosed new aspects of the blazar
phenomenology, leading to a much more robust understanding of the mechanisms
underlying their emission, and offering clues for the energetics of their
relativistic jets. I review these aspects, and propose that all the diversity
in the blazar phenomenology depends on only one parameter. I also suggest that
some of the blazar characteristics can be explained by the internal shock
scenario, as proposed to explain the emission from gamma-ray bursts.
