The objectives of the Mars Reconnaissance Orbiter (MRO) Radio Science Gravity Investigation are to improve knowledge of the static structure and characterize the temporal variability of the Martian gravitational field relevant to the planet's internal dynamics, the structure and dynamics of the atmosphere, and the orbital evolution of spacecraft at Mars. The investigation will utilize range rate and range measurements from X-band and, when available, Ka-band tracking systems of the MRO spacecraft. MRO will enable a considerable improvement in the spatial resolution and quality of Mars' global gravity field. The low orbital periapsis of MRO (∼255 km) will yield gravity maps suitable for study of regional (∼10² km) structure of the crust and lithosphere. The addition of tracking data from the Mars Global Surveyor and Mars Odyssey spacecraft, also currently orbiting Mars, will be useful in decorrelating errors in spherical harmonic coefficients of the gravity field that will improve the quality of the static field. Studies of the low-degree gravity field combined with measurements of rotational dynamics will permit insight about the structure of Mars' deep interior. Changes in the low-degree spherical harmonic coefficients of the Martian gravity field and in polar mass anomalies will be used to track the seasonal cycle of CO₂ exchange with the surface. Measurements of spacecraft drag will be used to estimate density variations in the atmosphere relevant to weather patterns and aerobraking of future spacecraft. Tracking observations will also be used to improve the ephemeris of Mars and the masses of the Martian moons.