  Beppo}SAX contributed substantially to our understanding of the physics of
blazars. This has been made possible mainly by its wide energy range and
especially by its high energy detector. Together with the information coming
from still higher energies we know at last the entire spectral energy
distribution (SED) of blazars. Different subclasses of blazars have different
SEDs, which seem to form a sequence, whose main parameter is the bolometric
luminosity. Physically, the blazar sequence can be the result of different
cooling rates by those electrons emitting most of the radiation we see. Blazars
are among the most active sources we know of, and the coordinated variability
at high energies gives very important clues about the physics of their jets:
initially, they must transport energy in a dissipationless way. They radiate
most of the entire bolometric luminosity we see at a preferred distance of a
few hundreds of Schwarzchild radii.For powerful blazars, the emitted radiation
must be a small fraction of the power transported by the jet, since the bulk of
it is required to energize the radio lobes. These are the jets which likely
have bulk relativistic speeds up to hundreds of kiloparsecs, as suggested by
the bright X-ray knots detected by Chandra in many extended jets.
