This is a catalog of all known quasi-stellar objects (QSO's) with measured emission redshifts and BL Lac objects, complete to 1992 December 31. The catalog contains 7312 objects, nearly all QSOs including about 90 BL Lac objects. The catalog and references contain extensive information on names, positions, magnitudes, color, emission-line redshifts, absorption, variability, polarization, and X-ray, radio, and infrared data. A key in the form of subsidiary tables enables the reader to relate the name of a given object to its coordinate name which is used throughout the catalog.