Gaia is an ESA astrometric mission launched end of 2013 for a nominal mission of five years. It is providing unprecedented astrometry (parallaxes and proper motions) and spectrophotometry for more than 1 billion sources brighter than G=20.7 mag.
It also provides spectrocopy for the brightest onces. By providing 3D spatial and velocity distributions of the stars combined with their astrophysical properties, Gaia is revolutionizing our knowledge of the Milky Way formation history and of stellar evolution. But it is also observing solar system objects, local group resolved stars, unresolved galaxies, quasars, it is alerting on photometric transients and will allow to perform relativistic tests.
I will present the content of the second Gaia data release together with a few of the many examples of its scientific exploitation, from survey calibration to dark matter constraints.