A catalogue of quasars and active nuclei:: 12th edition

Aims. This catalogue is aimed at presenting a compilation of all known AGN in a compact and convenient form and we hope that it will be useful to all workers in this field. Methods. Like the eleventh edition, it includes position and redshift as well as photometry ( U, B, V) and 6 cm flux densities when available. We now give 20 cm rather than 11 cm flux densities. Results. The present version contains 85 221 quasars, 1122 BL Lac objects and 21 737 active galaxies ( including 9628 Seyfert 1s), almost doubling the number listed in the 11th edition. We also give a list of all known lensed and double quasars.