  This paper documents the sixteenth data release (DR16) from the Sloan Digital
Sky Surveys; the fourth and penultimate from the fourth phase (SDSS-IV). This
is the first release of data from the southern hemisphere survey of the Apache
Point Observatory Galactic Evolution Experiment 2 (APOGEE-2); new data from
APOGEE-2 North are also included. DR16 is also notable as the final data
release for the main cosmological program of the Extended Baryon Oscillation
Spectroscopic Survey (eBOSS), and all raw and reduced spectra from that project
are released here. DR16 also includes all the data from the Time Domain
Spectroscopic Survey (TDSS) and new data from the SPectroscopic IDentification
of ERosita Survey (SPIDERS) programs, both of which were co-observed on eBOSS
plates. DR16 has no new data from the Mapping Nearby Galaxies at Apache Point
Observatory (MaNGA) survey (or the MaNGA Stellar Library "MaStar"). We also
preview future SDSS-V operations (due to start in 2020), and summarize plans
for the final SDSS-IV data release (DR17).
