The HEAO A-1 X-Ray Source Catalog is a compilation of data for 842 sources detected with the U. S. Naval Research Laboratory Large Area Sky Survey Experiment flown aboard the HEAO 1 satellite. The data include source identifications, positions, error boxes, mean X-ray intensities, and cross identifications to other source designations. Introduction: The primary objective of the Naval Research Laboratory (NRL) Large Area Sky Survey Experiment (LASS) flown aboard the HEAO 1 satellite was to conduct an all-sky survey for the brightest X-ray sources in the energy range 0.25 to 25 keV. The instrumentation consisted of an array of large proportional counter modules with collimators of varying fields of view and with sufficient sensitivity to detect sources as faint as 0.25 mu.Jy at 5 keV, assuming a Crab-like spectrum (1.1 muJy at 5 keV = 1 UFU for a Crab-like spectrum). Full sky coverage was achieved in the first 6 months of the mission by continuously scanning great circles perpendicular to the Earth-Sun line. The HEAO A-1 catalog results from the 6-month survey and, thus, covers the whole sky. For additional information concerning the NRL LASS instrument, the data analysis procedures, characteristics and limitations of the source data, and a discussion of X-ray source classes, the source publication should be consulted.