Dawn is the first mission to orbit a main belt asteroid and the first scientific mission to use ion propulsion. Major objectives of this mission include mapping of the surfaces of 4 Vesta and 1 Ceres, determining its topography from stereo measurements, determining its mineralogy, measuring its elemental composition and obtaining gravity data. This book describes the Dawn mission, its exploration and scientific objectives, the instruments that accomplish those objectives, the operations plan and the education and outreach plan. It is directed to those studying asteroids and the evolution of the solar system.