The Legacy Survey is producing an inference model catalog of the sky from a set of optical and infrared imaging data, comprising 14,000 square deg of extragalactic sky visible from the northern hemisphere in three optical bands (g,r,z) and four infrared bands. The sky coverage is approximately bounded by -18deg %3C delta %3C +84deg in celestial coordinates and |b||b| > 18deg in Galactic coordinates. The DECam Legacy Survey is providing these data in the equatorial region at delta %3C +30deg using the Dark Energy Camera on the Blanco Telescope. The color images are based on the g,r,z filters. Data Release 3 (DR3) is the third public data release of images and catalogs for the DECam Legacy Survey (DECaLS). Images from DECaLS g,r,z-band observations (NOAO survey program 0404; https://www.noao.edu/perl/abstract?2014B-0404) are included from August 2014 through March 2016. DR3 also includes DECam data from a range of non-DECaLS surveys, including observations that were conducted from September 2012 to March 2016. In total, the optical data covers a disjoint footprint with 4300 square deg in g-band, 4600 square deg in r-band and 8100 square deg in z-band, of which 4200 square deg has been observed in all three optical filters.