The Gaia cornerstone mission of the European Space Agency, scheduled for launch in mid-2013, is expected to produce a breakthrough in our understanding of the Galaxy, providing a full characterisation of all sources by extremely accurate astrometry and complementary spectral data. The continuous scanning of the sky and the fully automated selection of the sources also ensure that nearly all Solar System objects brighter than V=20 will be observed by Gaia. We describe the expectations of the mission in Solar System science and the peculiar properties of asteroid data, requiring appropriate data reduction procedures currently being implemented. Recent estimates of the number of observed sources and other statistical properties of the sample are presented. ► The number of asteroids Gaia will detect. ► The accuracy budget is explored for different object categories. ► The on-board windowing strategy.