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If blazars are such a special orientation of AGN, they are clearly a minority event, and an accidental one at that. So understanding blazars for the sake of blazars alone is not especially important. Because of their special orientation, however, blazars offer a direct probe of the unknown and very interesting physics of energy production in the centers of AGN, probably associated with the presence of a supermassive black hole. In this sense, understanding blazar emission may be more fundamental - more directly related to the physics of the central black hole - than the distribution of broad-emission-line clouds or even the thermal radiation from an accretion disk.

The ultimate goal of blazar research is to learn how energy is extracted from the black hole. In a more immediate sense, the goal is to understand how relativistic jets, which represent a tremendous amount of kinetic energy, are formed and accelerated. We are still at a very early stage in this endeavor, trying at this point simply to understand how much energy is involved and what the physical state of the jet is. Specifically, we are trying to measure the energy densities of particles, magnetic fields, and radiation, as well as the velocity field of the jet. These must be inferred since the observed radiation depends strongly on the amount of relativistic beaming, as well as the intrinsic properties of the jet.

Were we able to resolve the jets at wavelengths from radio through gamma-rays, this problem would be much simpler. But because the scales involved are probably 10-8-10-5 arcsec for regions emitting at or above optical frequencies, current technology precludes direct imaging. Instead, we infer the jet structure from variability as a function of wavelength. Time-scales for the fastest (observed) variability range from minutes at the highest energies to days or weeks at optical or radio wavelengths. This talk describes the results from recent multiwavelength monitoring campaigns on a few blazars, which are leading to important progress in this area.