Gaia is an ESA mission to build a census of our Milky Way Galaxy. This is done with asuite of three instruments combining two fields of view into a single focal plane.On-board detection of all sources will ensure a bias free survey down to the 20thmagnitude. In addition to astrometry also photometry is done down to the 20th magnitude.The third, spectroscopic instrument will provide radial velocities down to the 17thmagnitude of the Galactic stellar population. Currently the scientific requirements onGaia are largely met except for bright stars for which in astrometry additional effortsare needed to squeeze the remaining μarcsecs out of the positionalinformation error budgets. In the mid-magnitude range (15 mag) the end of mission parallaxerrors are from 10 to 25 μarcsec and photometry errors are between 5 and16 mmag. Radial velocities are better than 1 km s-1 for the bright stars witherrors increasing to 15 km s-1 for the faintest ones. At the moment there areno unsolvable technical challenges on the table and Gaia is progressing toward the launchin 2012.