This paper presents the 12th edition of a comprehensive catalogue of quasars and active nuclei (AGN), compiled by M.-P. Véron-Cetty and P. Véron from the Observatoire de Haute Provence, CNRS. The catalogue includes 85,221 quasars, 1,122 BL Lac objects, and 21,737 active galaxies (including 9,628 Seyfert 1s), nearly doubling the number from the 11th edition. It covers quasars with measured redshifts known to the authors as of January 1, 2006, and provides absolute magnitudes and 20 cm flux densities for each object. The catalogue is intended for researchers in the field and is not suitable for statistical analysis due to its incomplete nature. The introduction highlights the historical development of quasar catalogs, noting the significant increase in known quasars following the release of the 2dF and Sloan Digital Sky Survey (SDSS) catalogs. The catalogue includes detailed descriptions of the tables, columns, and references used, as well as corrections for cosmological effects on absolute magnitudes.This paper presents the 12th edition of a comprehensive catalogue of quasars and active nuclei (AGN), compiled by M.-P. Véron-Cetty and P. Véron from the Observatoire de Haute Provence, CNRS. The catalogue includes 85,221 quasars, 1,122 BL Lac objects, and 21,737 active galaxies (including 9,628 Seyfert 1s), nearly doubling the number from the 11th edition. It covers quasars with measured redshifts known to the authors as of January 1, 2006, and provides absolute magnitudes and 20 cm flux densities for each object. The catalogue is intended for researchers in the field and is not suitable for statistical analysis due to its incomplete nature. The introduction highlights the historical development of quasar catalogs, noting the significant increase in known quasars following the release of the 2dF and Sloan Digital Sky Survey (SDSS) catalogs. The catalogue includes detailed descriptions of the tables, columns, and references used, as well as corrections for cosmological effects on absolute magnitudes.