GOCE will map the global variations in Earth's gravity with extreme detail and provide a unique model of the gravity field and geoid. The geoid is the surface of equal gravitational potential defined by the gravity field and is crucial for improving our understanding of ocean circulation, sea-level change and terrestrial ice dynamics, all of which are affected by climate change. GOCE-derived data will also provide new insight into processes occurring in the lithosphere and upper mantle. In addition, data will be used for practical applications such as surveying and levelling.