GENIUS is designed to boost the impact of the next European breakthrough in astrophysics, the Gaia astrometric mission. Gaia is an ESA Cornerstone mission scheduled for launch in October 2013 and aims at producing the most accurate andcomplete 3D map of the Milky Way to date. A pan-European consortium named DPAC is working on the implementation of the Gaia data processing, of which the final result will be a catalogue and data archive containing more than one billion objects. The archive system containing the data products will be located at the European Space Astronomy Centre (ESAC) and will serve as the basis for the scientific exploitation of the Gaia data. The design, implementation, and operation of this archive are a task that ESA has opened up to participation from the European scientific community. GENIUS is aimed at significantly contributing to this development based on the following principles: an archive design driven by the needs of the user community; provision of exploitation tools to maximize the scientific return; ensuring the quality of the archive contents and the interoperability with existing and future astronomical archives (ESAC, ESO, ...); cooperation with the only other two astrometric missions in the world, nanoJASMINE and JASMINE (Japan); and last but not least, the archive will facilitate outreach and academic activities to foster the public interest in science in general and astronomy in particular. GENIUS fits seamlessly into existing Gaia activities, exploiting the synergies with ongoing developments. Its members actively participate in these ongoing tasks and provide an in-depth knowledge of the mission as well as expertise in key development areas.Furthermore, GENIUS has the support of DPAC, several Gaia national communities in the EU member states, and will establish cooperation with the Japanese astrometric missions already mentioned.