The improved flux sensitivity of VERITAS will permit the detection of weaker sources of VHE emission. Its lower energy threshold will permit the viewing of objects further from Earth (the optical depth for pair production decreases rapidly with decreasing energy) and those objects which have spectral cut-offs below the sensitive range of existing Cherenkov telescopes. Based on the multi-wavelength spectra of Mrk 421 and Mrk 501, we expect that VERITAS will detect 30 or more X-ray selected BL Lacs. This should permit class-wide studies of this type of blazar that actually appears to be most efficient at emitting VHE photons. An exciting prospect is that VERITAS will detect ``Extreme BL Lacs,'' a hypothetical class of object whose power output actually peaks in the TeV range ([Ghisellini 1999]). These objects would be difficult to identify through traditional means (radio, optical, X-ray surveys) because of their low luminosity in those wavebands, but a detection at VERITAS energies would firmly identify them as blazars.
EGRET sources associated with AGN now number at least 66 ([Hartman et al. 1999]) and span a range of redshifts from z = 0.03 - 2.28, while only six AGN have been detected above 300GeV. The most likely causes of this disparity are intrinsic cut-offs in the source spectra and, for the more distant sources, attenuation of the TeV gamma-rays by pair-production with background IR radiation. The low energy threshold and good sensitivity of VERITAS will overcome these hurdles and lead to the detection of approximately 15 of the EGRET AGN, more if GLAST or all-sky X-ray monitors indicate when these objects are in high emission states. By measuring the ends of the spectra for several EGRET sources, VERITAS can help determine what particles produce the gamma-ray emission in blazars (on average, electrons should show cut-offs which correlate with lower energy spectra, protons would not show a simple correlation). In addition, recent models to unify the different classes of blazar ([Ghisellini et al. 1998]; [Georganopoulos & Marscher 1998]) can be significantly refined or eliminated once the shapes and locations of the blazar spectra are measured. VERITAS is in a unique position to make these measurements, providing better photon statistics than space-based telescopes at these energies and superior energy resolution and sensitivity relative to other ground-based telescopes.