The Hipparcos space astronomy mission was dedicated to the very accurate measurement of star positions and star motions in space. The satellite was designed, built, and operated under the responsibility of the European Space Agency. It was launched in August 1989 and operated until mid-1993. The two resulting star catalogs were completed and published in 1997: the Hipparcos Catalogue is a high-accuracy compilation of nearly 120,000 star positions, distances, and motions; the Tycho Catalogue is a lower-accuracy catalog of slightly more than 1 million stars. Together they represent astronomers' best understanding of the spatial distribution, space motion, and corresponding physical properties of stars in the solar neighborhood. The experiment was carried out by a collaboration of about 200 scientists.