(1) Lund Observatory, Sweden
(2) Observatoire de Paris, Section de Meudon, France
Hipparcos brings astrometric and photometric data of an unprecedent quality for more than 100000 stars. Many branches of Astronomy and Astrophysics will benefit highly from this new knowledge. We review the main topics where dramatic changes can be anticipated: reference frames, absolute proper motions and their implications for the dynamics of solar system objects, stellar systems and stellar populations; stellar and galactic physics; new knowledge on the very nearby stars and consequences for the HR diagram and the determination of the luminosity function; calibration of distance scale indicators.
We also outline the perspectives opened by a future project such as GAIA, proposed for the ESA Horizon 2000+ programme, with an expected astrometric accuracy of 1 to 10 microarcsec and simultaneous multi-band photometry.