The Dawn mission journeys to the center of the main asteroid belt to orbit and explore the two most massive main belt asteroids, Vesta and Ceres. Dawn aims to increase our understanding not just of the present state of these two bodies, but also of the conditions during the time of their formation. It attempts this through achieving a set of measurement objectives in which the physical properties of these asteroids such as mass, slopes, size, density, and spin state are accurately determined, and in which the mineralogical and elemental composition of the surface and near-surface material are probed. Dawn employs ion propulsion technology to enable a modestly-sized launcher to start a moderately-sized spacecraft on its journey, to not only reach the two massive asteroids but also to orbit them, descending to near the surface. Unlike most orbital missions, the initial (Vesta) phase must be completed with sufficient reserves and within a time window that later allows Dawn to explore Ceres. Dawn carries a redundant framing camera, a visible and near-IR spectrometer, a gamma ray and neutron spectrometer, and achieves high-accuracy radiometric and optical navigation to enable gravity field determination. The spacecraft was developed by Orbital Sciences Corporation under the management of the Jet Propulsion Laboratory for the National Aeronautics and Space Administration. Dawn is a Principal Investigator-led mission of the Discovery Program. The PI institution, the University of California, Los Angeles, manages directly the science team, the Dawn Science Center, and the Education and Public Outreach program.