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We present a catalog of 1,172,157 quasar candidates selected from thephotometric imaging data of the Sloan Digital Sky Survey (SDSS). The objectsare all point sources to a limiting magnitude of i=21.3 from 8417 sq. deg. ofimaging from SDSS Data Release 6 (DR6). This sample extends our previouscatalog by using the latest SDSS public release data and probing both UV-excessand high-redshift quasars. While the addition of high-redshift candidatesreduces the overall efficiency (quasars:quasar candidates) of the catalog to~80%, it is expected to contain no fewer than 850,000 bona fide quasars -- ~8times the number of our previous sample, and ~10 times the size of the largestspectroscopic quasar catalog. Cross-matching between our photometric catalogand spectroscopic quasar catalogs from both the SDSS and 2dF Surveys, yields88,879 spectroscopically confirmed quasars. For judicious selection of the mostrobust UV-excess sources (~500,000 objects in all), the efficiency is nearly97% -- more than sufficient for detailed statistical analyses. The catalog'scompleteness to type 1 (broad-line) quasars is expected to be no worse than70%, with most missing objects occurring at z<0.7 and 2.5<z<3.0. In addition toclassification information, we provide photometric redshift estimates(typically good to Delta z +/- 0.3 [2 sigma]) and cross-matching with radio,X-ray, and proper motion catalogs. Finally, we consider the catalog's utilityfor determining the optical luminosity function of quasars and are able toconfirm the flattening of the bright-end slope of the quasar luminosityfunction at z~4 as compared to z~2.

Efficient Photometric Selection of Quasars from the Sloan Digital Sky Survey: II. ~1,000,000 Quasars from Data Release Six