Abstract The author discusses the relationship between X and γ radiation and radio to optical emission in blazars based on recent observations. The availability of densely-sampled light curves at several wavebands for several quasars, BL Lacertae, and two radio galaxies demonstrates that a strong connection exists between high and low frequency emission. The relativistic jet provides the most straightforward explanation of this connection. In the radio galaxies, temporary decreases in the X-ray flux from the central engine precede the appearance of bright superluminal knots in the radio jet. The combination of multiwaveband light curves and millimeter-wave imaging with very long baseline interferometry, along with polarization measurements whenever possible, can map the emission regions and lead to more accurate theoretical descriptions of the physical processes in blazars than has been possible in the past.
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