BL Lac objects and relativistic beaming

General arguments for relativistic beaming in BL Lac objects are reviewed. These include overproduction of X-rays and fast time variability. Comments are made about the relationship of the X-ray continuum to that at lower frequencies, and observational evidence for and against continuum radiation being relativistically beamed is discussed. Finally, there is discussion of the influence of geometrical effects on predictions for time variability as a function of frequency in the context of inhomogeneous synchrotron self-Compton jet models.