  The Gaia astrometric mission - the Hipparcos successor - is described in some
detail, with its three instruments: the two (spectro)photometers (BP and RP)
covering the range 330-1050 nm, the white light (G-band) imager dedicated to
astrometry, and the radial velocity spectrometer (RVS) covering the range
847-874 nm at a resolution R \simeq 11500. The whole sky will be scanned
repeatedly providing data for ~10^9 point-like objects, down to a magnitude of
V \simeq 20, aiming to the full 6D reconstruction of the Milky Way kinematical
and dinamical structure with unprecendented precision. The horizon of
scientific questions that can find an answer with such a set of data is vast,
including besides the Galaxy: Solar system studies, stellar astrophysics,
exoplanets, supernovae, Local group physics, unresolved galaxies, Quasars, and
fundamental physics. The Italian involvement in the mission preparation is
briefly outlined.
