Book excerpt: Precise and continuous tracking with multi-satellite systems of aircraft andlow flying satellites, accurate airborne measurement of gravity and gravity gradients, and satellite gradiometry have fundamentally changed our view on the de- termination of the Earth's gravity field. The papers in this volume describe these techniques in detail. The ideas are presentedas complementary, and are used to develop new theoretical concepts of gravity field analysis. Computatio- nal models using these techniques are also discussed and are tested in simulations. The papers presented in this volume are the result of an IAG symposium held during the XX General Assembly of the Inter- national Union of Geodesy and Geophysics in Vienna, Austria, August 11-24, 1991.