BL Lacs, Highly Polarized Quasars (HPQs) and Optically Violent Variables (OVVs) are classed as blazars. Based on the multifrequency spectral properties of these objects we have classified the blazars into two groups which are as follows:

• – Group I - BL Lacs

  BL Lac objects are soft X–ray sources (Hardness ratio is less than 5) with steep and flat spectral indices in the X–ray and ultraviolet bands, respectively. They are relatively less polarized (in the optical band) and low luminous objects (Mabs < −23). Radio to X–ray spectra of BL Lacs can be fitted with a single parabolic curve and these objects radiate most of their energies in the X–ray band (radio through X–ray frequencies).

• – Group II - HPQs/OVVs

  HPQs and OVVs are hard X–ray sources (Hardness ratio is greater than 5) with flat and steep spectral indices in the X–ray and ultraviolet bands, respectively. These are highly polarized and highly luminous (Mabs > −23) objects. Radio to X–ray continuum emission spectra of HPQs/OVVs can be fitted with two parabolic curves with the spectral break between UV and X–ray bands and these objects radiate most of their energies in the infrared band.