Rosetta is European Space Agency (ESA) Horizon 2000 cornerstone mission number 3 designed to rendezvous with Comet 67 P/Churyumov-Gerasimenko, drop a probe on the surface, study the comet from orbit, and fly by at least one asteroid en route. The principal goals are to study the origin of comets, the relationship between cometary and interstellar material and its implications with regard to the origin of the solar system. Its scientific objectives to achieve these goals are: global characterization of the nucleus, determination of dynamic properties, surface morphology and composition; determination of the chemical, mineralogical and isotopic compositions of volatiles and refractories in a cometary nucleus; determination of the physical properties and interrelation of volatiles and refractories in a cometary nucleus; study of the development of cometary activity and the processes in the surface layer of the nucleus and the inner coma (dust/gas interaction); global characterisation of asteroids, including determination of dynamic properties, surface morphology and composition.