The Proceedings of IAU S248 reflect the state-of-the-art in the field of astrometry, summarizing the scientific achievements at the tenth anniversary of the Hipparcos and Tycho Catalogue release. It shows the latest achievements in ground-based astrometry and details the progress of second-generation astrometric satellites. Currently, the highest accuracies at a micro-arc-second level are reached by interferometric techniques, especially at radio wavelengths. Establishing and maintaining the celestial reference frame at this level, within a relativistic framework, has been identified as one...