GOCE (Gravity Field and Steady-State Ocean Circulation Explorer) is a single satellite mission orbiting the Earth at a very low altitude of just 250 km. It is the first space mission to employ the concept of gradiometry to map the Earth's gravity field with unprecedented detail. Since the gravity measurements taken by GOCE reflect density variations in the inside of the Earth, the resulting data will lead to new insights into the physics and dynamics of the Earth's crust and upper mantle, potentially leading to an improvement in the prediction of events such as earthquakes and volcanic activity.