According to the recommendations of the Paris IAU Secretariat, the present triennial commission report is intended to put special emphasis on outstanding achievements around the main objectives of the commission rather than on abstracting all the literatures relevant to the commission. The highlights of the commission during the triennium under review have been the establishment of the conventional stellar reference frame FK5, an intensive effort in extension of the stellar reference frame to a celestial network of higher star densities and fainter magnitudes, and the launch of the astrometric satellite HIPPARCOS, as are described in this report.