Many economically important mineral and petroleum discoveries can be directly or indirectly credited to the aeromagnetometer. Magnetic methods are most important for geological reconnaissance and mapping. Also, deep crustal and upper-mantle studies can be made from results. Spin-precession magnetometers, developed in the past five years, include the proton-precession magnetometer, the alkali-vapor rubidium and cesium instruments, and the metastable-helium magnetometer. Modern navigational and interpretational techniques have improved usefulness of aeromagnetic surveying. Diurnal effects may be corrected, and their behavior is becoming understood. Interpretative systems may be divided into qualitative inspection, profile analysis, and map methods. Numerous schemes have been proposed for analytic purposes; principal methods are reviewed.