OSIRIS (OH-Suppressing InfraRed Integral-field Spectrograph) is a new facility instrument for the Keck Observatory. Starting in 2004, it will provide the capability of performing three-dimensional spectroscopy in the near-infrared z, J, H, and K bands at the resolution limit of the Keck II telescope, which is equipped with adaptive optics and a laser guide star. The innovative capabilities of OSIRIS will enable many new observing projects. Galaxies in the
early Universe will be among the most interesting targets for OSIRIS, which will perform detailed studies of their stellar content and dynamical properties. In more exotic objects, such as quasars, radio galaxies, and more nearby active galactic nuclei, OSIRIS can elucidate the relation of the central black hole to the properties of the host galaxy, and the mechanism by which gas
is fed into the central engine. In the center of our own Galaxy, it will be possible to search for signatures of interaction between the massive black hole and stars in its immediate vicinity. Closer to home, OSIRIS will perform spectroscopic observations of young stars and their environment, and of brown dwarfs. Imaging spectroscopy of the giant planets, their moons, and asteroids will shed new light on meteorology, mineralogy, and volcanism in the Solar System. OSIRIS observations of Kuiper Belt objects will provide sufficient sensitivity to establish their surface composition, which will contribute substantially to our understanding of the history of the Solar System.