The second Gaia data release, Gaia DR2, encompasses astrometry, photometry, radial velocities, astrophysical parameters (stellar effective temperature, extinction, reddening, radius, and luminosity), and variability information for up to 1.6 billion stars. Gaia DR2 is based on the first 22 months of the nominal, five-year mission, processed by the Gaia Data Processing and Analysis Consortium (DPAC).