According to unified schemes for blazars, BL Lac objects are dominated by relativistic jets pointing along the line of sight. Their plane-of-the-sky counterparts are likely to be low-luminosity radio galaxies, which are generally luminous ellipticals that lie preferentially in clusters of galaxies. As part of a test of unification, and in order to improve our understanding of BL Lac objects, we are using the Hubble Space Telescope WFPC2 to image a complete sample of radio-selected BL Lac objects, having redshifts as high as z ~ 1, at far better spatial resolution than is possible from the ground. Our primary goals are to study the host galaxies and the environments of these unusual AGN. The limiting factor in detecting host galaxies is the subtraction of the bright nuclear light, which is smeared by the point spread function (PSF) of the telescope. We have employed a new observing technique, rolling the telescope between images, that provides an additional means of estimating the PSF. Here we present preliminary results for a subset of our sample objects, including examples in and out of galaxy clusters.