Gaia is an ESA mission that is radically changing our view of the Milky Way. It is providing astrometry, photometry, and spectroscopy for over 10^9 sources with unprecedented quality. The talk is divided in two parts. In the first one I will describe the general characteristics and achievements of Gaia. In the second half I will describe the involvement of our group in the mission with respect to its astrometric and photometric calibration and the study of OB stars, stellar clusters and associations, and Galactic structures.