The gravity studies addressed at this site are those that involve geophysical mapping and interpretation of features in the Earth’s lithosphere. The emphasis is on the upper crust of the Earth that extends to depths of about 20 km, because it is this region where gravity and magnetic data can best help delineate geologic features related to natural hazards, natural resources, and tectonic events such as the formation of mountain belts. Such studies provide elegantly straightforward demonstrations of the applicability of classical physics and digital processing to the solution of a variety of geological problems. These problems vary in scale from very local investigations of features such as faults to regional studies of the structure of tectonic plates. In addition to applications of gravity measurements the site also provides information about techniques and measurements and the various corrections that must be applied. Density and density measurements are discussed and a table of standard densities is included. Links are provided to sources for datasets and software.