The Rosetta spacecraft will rendez-vous with comet Wirtanen round 2011 and will study it for a period of nearly two years, thus providing a unique opportunity to monitor its behaviour over a wide range of distances from the Sun. A plasma and wave package, the Rosetta Plasma Consortium, RPC, will be part of the Rosetta orbiter payload. RPC is a highly integrated package that consists of five sensors: the Langmuir Probe, LAP, the Ion and Electron Sensor, IES, the Ion Composition Analyzer, ICA, the Fluxgate Magnetometer, MAG, and the Mutual Impedance Probe, MIP. RPC also includes the common instrument control, spacecraft interface, and power management unit, PIU, plus the Electrical Ground Support Equipment, EGSE. The prime objectives of RPC are to investigate: (1) the physical properties of the cometary nucleus and its surface, (2) the inner coma structure, dynamics, and aeronomy, (3) the development of cometary activity, and the microscopic and macroscopic structure of the solar-wind interaction region as well as the formation and development of the cometary tail. In addition, the planned asteroid, possibly Otawara and Siwa, flybys will provide an excellent opportunity to study in detail the physics of the solar wind-asteroid interaction. The magnetic and electric conductivity properties of the asteroid will also be studied.