The proper and efficient operation of the Hipparcos satellite requires positions within 1.5 arcsec at the 1989 epoch for the 100-120 000 programme stars. The first steps of the preparation have been the identification of the proposed stars in the well-known astrometric catalogues and the output of successive lists of ‘non-astrometric’ stars not belonging to these catalogues. Ground-based observations needed to supplement the presently available data, which are now under way, are also described.