The Third Data Release of the Beijing?Arizona Sky Survey

The Beijing?Arizona Sky Survey (BASS) is a wide and deep imaging survey that covers a 5400 deg(2) area in the northern Galactic cap with the 2.3 m Bok telescope using two filters (g and r bands). The Mosaic z-band Legacy Survey (MzLS) covers the same area in the z band with the 4 m Mayall telescope. These two surveys will be used for spectroscopic targeting by the Dark Energy Spectroscopic Instrument (DESI) in the northernmost portion of the DESI footprint. This paper describes the third data release (DR3) of BASS, which contains the photometric data from all BASS and MzLS observations from 2015 January until the completion of BASS in 2019 March. The median astrometric precision relative to Gaia positions is about 17 mas and the median photometric offset relative to the Pan-STARRS1 photometry is within 5 mmag. The median 5? AB magnitude depths for point sources are 24.2, 23.6, and 23.0 mag for the g, r, and z bands, respectively. The photometric depth within the survey area is highly homogeneous, and the difference between the 20% and 80% depth is less than 0.3 mag. The DR3 data, including raw data, calibrated single-epoch images, single-epoch photometric catalogs, stacked images, and co-added photometric catalogs, are publicly accessible at .