The USNO-B catalog is an all-sky catalog containing positions, proper motions, magnitudes in various optical passbands, and star/galaxy estimators for 1,042,618,261 objects derived from 3,643,201,733 observations. The data were obtained from scans of 7,435 Schmidt plates taken over the last 50 years. USNO-B1.0 provides all-sky coverage, completeness down to V = 21, 0.2 arcsecond astrometric accuracy at J2000, 0.3 magnitude photometric accuracy in up to five colors, and 85% accuracy for distinguishing stars from non-stellar objects. The catalog is compiled from the merged lists of detections from the digitization of photographic sky survey plates by the Precision Measuring Machine (PMM) located at the U.S. Naval Observatory Flagstaff Station. The catalog includes five complete coverages of the Northern sky and four of the Southern sky, and contains a mixture of colors and epochs. The catalog was compiled from the merged lists of detections, and presents position, proper motion, magnitudes in various colors, star-galaxy classification, and various uncertainty estimators for 1,042,618,261 distinct objects. The catalog is not submitted for publication in a journal, but the digital distribution can be found at http://www.nofs.navy.mil and other sites. USNO-B is the next step in the sequence of catalogs that started with UJ1.0 (Monet et al. 1994), USNO-A1.0 (Monet et al. 1996) and USNO-A2.0 (Monet et al. 1998). USNO-B is a 3-color, 2-epoch catalog. The catalog includes data from 7,435 Schmidt plates, and the missing fields are numbers 1 and 646 in the SERC-I survey. The catalog includes data from 937 POSS-I fields. The plates involved in USNO-B are about 60% of the Schmidt plates scanned by the PMM. Data from the other plates (rejected, Luyten's, etc.) will be included in future USNO catalogs. The PMM uses a 2-dimensional charge coupled device (CCD) camera as its sensor. A Schmidt plate is digitized in 588 separate exposures, and each produces a 1312 by 1032 image digitized with 8-bit resolution. The CCDs have 6.8 by 6.8 micron pixels, a 100% fill factor, and are read at 10 million pixels per second. A complete exposure cycle takes about 0.5 seconds including theThe USNO-B catalog is an all-sky catalog containing positions, proper motions, magnitudes in various optical passbands, and star/galaxy estimators for 1,042,618,261 objects derived from 3,643,201,733 observations. The data were obtained from scans of 7,435 Schmidt plates taken over the last 50 years. USNO-B1.0 provides all-sky coverage, completeness down to V = 21, 0.2 arcsecond astrometric accuracy at J2000, 0.3 magnitude photometric accuracy in up to five colors, and 85% accuracy for distinguishing stars from non-stellar objects. The catalog is compiled from the merged lists of detections from the digitization of photographic sky survey plates by the Precision Measuring Machine (PMM) located at the U.S. Naval Observatory Flagstaff Station. The catalog includes five complete coverages of the Northern sky and four of the Southern sky, and contains a mixture of colors and epochs. The catalog was compiled from the merged lists of detections, and presents position, proper motion, magnitudes in various colors, star-galaxy classification, and various uncertainty estimators for 1,042,618,261 distinct objects. The catalog is not submitted for publication in a journal, but the digital distribution can be found at http://www.nofs.navy.mil and other sites. USNO-B is the next step in the sequence of catalogs that started with UJ1.0 (Monet et al. 1994), USNO-A1.0 (Monet et al. 1996) and USNO-A2.0 (Monet et al. 1998). USNO-B is a 3-color, 2-epoch catalog. The catalog includes data from 7,435 Schmidt plates, and the missing fields are numbers 1 and 646 in the SERC-I survey. The catalog includes data from 937 POSS-I fields. The plates involved in USNO-B are about 60% of the Schmidt plates scanned by the PMM. Data from the other plates (rejected, Luyten's, etc.) will be included in future USNO catalogs. The PMM uses a 2-dimensional charge coupled device (CCD) camera as its sensor. A Schmidt plate is digitized in 588 separate exposures, and each produces a 1312 by 1032 image digitized with 8-bit resolution. The CCDs have 6.8 by 6.8 micron pixels, a 100% fill factor, and are read at 10 million pixels per second. A complete exposure cycle takes about 0.5 seconds including the