GAIA is an astrometric mission approved as one of ESA's next two "cornerstone" science missions, with a planned launch by mid-2012. It aims to provide precise positional and radial velocity measurements for about one billion stars in the Milky Way and Local Group, enabling a detailed census of the Galaxy's structure, dynamics, and history. The mission will determine the star formation history, chemical evolution, and distribution of dark matter, while also studying stellar populations, binary stars, and planetary systems. GAIA will provide high-precision photometry and spectroscopy, enabling the study of stellar evolution, variability, and the cosmic distance scale. It will also contribute to the study of the Solar System, including minor bodies, asteroids, and near-Earth objects. The mission will test general relativity and cosmology through precise measurements of quasars and the Solar System's motion. GAIA's design includes two astrometric instruments, a radial velocity spectrometer, and a photometric system, with a focus on accuracy, stability, and long-term performance. The mission will provide a comprehensive survey of the Galaxy, the Local Group, and the universe, with a focus on understanding the formation and evolution of galaxies and the nature of dark matter. The mission will also contribute to the definition of the International Celestial Reference Frame and the study of fundamental physics, including the parameter γ in general relativity and the Solar quadrupole moment. The mission's design and scientific goals are based on a detailed study of the science case and instrument design, with a focus on achieving high accuracy and completeness in the data collected.GAIA is an astrometric mission approved as one of ESA's next two "cornerstone" science missions, with a planned launch by mid-2012. It aims to provide precise positional and radial velocity measurements for about one billion stars in the Milky Way and Local Group, enabling a detailed census of the Galaxy's structure, dynamics, and history. The mission will determine the star formation history, chemical evolution, and distribution of dark matter, while also studying stellar populations, binary stars, and planetary systems. GAIA will provide high-precision photometry and spectroscopy, enabling the study of stellar evolution, variability, and the cosmic distance scale. It will also contribute to the study of the Solar System, including minor bodies, asteroids, and near-Earth objects. The mission will test general relativity and cosmology through precise measurements of quasars and the Solar System's motion. GAIA's design includes two astrometric instruments, a radial velocity spectrometer, and a photometric system, with a focus on accuracy, stability, and long-term performance. The mission will provide a comprehensive survey of the Galaxy, the Local Group, and the universe, with a focus on understanding the formation and evolution of galaxies and the nature of dark matter. The mission will also contribute to the definition of the International Celestial Reference Frame and the study of fundamental physics, including the parameter γ in general relativity and the Solar quadrupole moment. The mission's design and scientific goals are based on a detailed study of the science case and instrument design, with a focus on achieving high accuracy and completeness in the data collected.