The USNO anticipates the release of the first large catalog from the Precision Measuring Machine (PMM) program in the summer of 1996. This catalog, called USNO-A1.0, is a catalog of 491,848,883 astrometric reference objects of which 19,524,809 have cross identifications in the Guide Star Catalog. The catalog data were derived from PMM scans of POSS-I O and E plates in the zones from -30 to +90, and from SERC-J and ESO-R plates in the zones from -90 to -35 degrees. The catalog contains all sources found to be coincident (within an aperture of 2 arcseconds) between the blue and red survey scans. The limiting magnitude should be at or near the nominal limiting magnitude quoted for the various surveys based on visual identification of sources. The only selection filter was spatial coincidence, and stars, galaxies, and other objects appear if they satisfy this requirement. USNO-A1.0 does not present source classification data, but these are expected to be included in future releases. Because the deep survey plates have relatively poor images for bright stars, pointers to all GSC objects brighter than 11(th) magnitude are included even if there was no matching PMM source. USNO-A1.0 adopts the astrometric reference frame of the GSC, but this will be replaced by the Hipparcos reference frame as soon as it enters the public domain. Because of the preliminary nature of the astrometric and photometric calibration, distribution of USNO-A1.0 should be confined to persons with an immediate need or those developing the software tools needed to access such catalogs. Its format follows the previously released UJ1.0 catalog.