  The DESI Legacy Imaging Surveys are a combination of three public projects
(the Dark Energy Camera Legacy Survey, the Beijing-Arizona Sky Survey, and the
Mayall z-band Legacy Survey) that will jointly image approximately 14,000 deg^2
of the extragalactic sky visible from the northern hemisphere in three optical
bands (g, r, and z) using telescopes at the Kitt Peak National Observatory and
the Cerro Tololo Inter-American Observatory. The combined survey footprint is
split into two contiguous areas by the Galactic plane. The optical imaging is
conducted using a unique strategy of dynamically adjusting the exposure times
and pointing selection during observing that results in a survey of nearly
uniform depth. In addition to calibrated images, the project is delivering a
catalog, constructed by using a probabilistic inference-based approach to
estimate source shapes and brightnesses. The catalog includes photometry from
the grz optical bands and from four mid-infrared bands (at 3.4, 4.6, 12 and 22
micorons) observed by the Wide-field Infrared Survey Explorer (WISE) satellite
during its full operational lifetime. The project plans two public data
releases each year. All the software used to generate the catalogs is also
released with the data. This paper provides an overview of the Legacy Surveys
project.
