The magnetic method plays an important role in mineral, petroleum, and geothermal exploration. It also has made important contributions to geologic mapping, structural geology, and plate-tectonic theory. In particular, magnetic measurements using aircraft provide a relatively inexpensive way to trace magnetic rock units beneath covered areas, to reveal the shape of subsurface magnetic bodies, and to interpolate subsurface geologic information between widely spaced seismic data and other localized geophysical measurements. Computerized interpretation procedures currently fall into two categores: techniques designed to enhance the data, which include various display and filtering procedures, and modeling experiments, which may be either forward (trial-and-error) or inverse in nature.