  The current status of leptonic jet models for blazars is reviewed.
Differences between the quasar and BL-Lac subclasses of blazars may be
understood in terms of the dominance of different radiation mechanisms in the
gamma-ray regime. Spectral variability patterns of different blazar subclasses
appear to be significantly different and require different intrinsic mechanisms
causing gamma-ray flares. As examples, recent results of long-term
multiwavelength monitoring of PKS 0528+134, 3C 279, and Mrk 501 are interpreted
in the framework of leptonic jet models. Short-term variability patterns give
important additional clues about the source geometry and the relevant radiation
mechanisms in blazars. Challenges for future observational efforts are
discussed.

Astrophysics