In the absence of seismic data, gravity and rotation provide
information on the interiors of planetary bodies. The Cassini mission
has completed four flybys devoted to the determination of Titan's
gravity field and carried out substantial SAR observations of the
surface, enabling a reliable estimate of the low degree harmonic
coefficients and an accurate determination of the satellite's
rotational state. The results are surprising.  Titan's gravity has
revealed significant anomalies and the satellite is not in synchronous
rotation. The maps of the geoid and gravity disturbances are
consistent with a mass deficiency on the bright area of Xanadu and a
mass excess on the opposite region of the satellite. The discovery of
gravity anomalies and the availability of the onboard radar altimeter
enable the construction of the large scale topography of the satellite
and correlations between gravity and topography, a crucial step in
unveiling Titan's interior structure.