Mass displacements and motions within and between individual components of the Earth system present dynamical processes which affect the rotation as well as the gravity field and the shape of the Earth. Whereas the space geodetic observation techniques monitor the fluctuations of Earth rotation, the changes of the gravity field and the sea level, geophysical models describe the mass displacements and motions inside the subsystems of the Earth (atmosphere, oceans, continental hydrology, etc.). Since the individual space geodetic procedures are sensitive to different components and subcomponents of the Earth system a common analysis and evaluation of all time series is aspired. In this context we have to look at the following issues:

• The geometric space geodetic techniques VLBI, SLR and GNSS monitor the variations of Earth rotation and allow to draw conclusions on integral mass displacements and motion;
  
  
• The gravity field satellite mission GRACE affords the evaluation of time variations of the Earth’s gravity field and therefore provides information over the underlying mass displacements in the atmosphere, the oceans and the continental hydrosphere;

• With the help of satellite altimetry sea level changes will be assigned which are caused by the fluctuations of sea water mass and volume.