Gaia is an ESA mission performing astrometry, photometry and spectroscopy of about one billion objects in our Milky Way galaxy and beyond. The extent and content of the Gaia Catalogues will enable major progress to be made in many fields of galactic and stellar astronomy. The prime industrial contractor, EADS Astrium, Toulouse, is manufacturing the spacecraft and its payload for launch in 2013. Parallel to the space segment development the ground segment is getting ready as well. The Mission Operations Centre in Darmstadt, the Science Operations Centre in Madrid and the Gaia Data Processing and Analysis Consortium having members in many institutes across Europe are all tackling the challenges imposed by the high scientific requirements of the mission. The Gaia observing principles, overall status and scientific performances will be outlined (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)