Abstract: The Earth's gravitational field is the integral response to the Earth's mass distribution. The rotation of the Earth turns gravitation into gravity. Thus, the Earth's gravity field contains both gravitational and rotational information. As an integral response the structure of the Earth's gravitational field represents an important source of information about our planet. Its knowledge is therefore an important source of information which is indispensible for a substantial progress in the geosciences in general and in geodesy, solid Earth physics, and oceanography in particular. The GOCE mission is based on a sensor fusion concept, combining GPS-based orbitography and satellite gravity gradiometry. The two sensors combined will deliver a gravity field with unprecedented accuracy and resolution. The underlying estimation process requires the solution of a superlarge and fully occupied system of about a 100 million equations. A smart solution strategy, based on a pre-conditioned conjugated gradient approach, has been demonstrated as a very powerful processing tool. The GOCE derived gravity field will provide a global height reference system at the centimeter level, combined with GPS positioning it will provide useful orthometric heights, combined with seismic data it will enable a significant advance in the understanding of the physics of the Earth's interior, and combined with altimeter data it will allow a precise determination of absolute ocean surface circulation on a global scale.