Developments which have led to an enormous increase in the use of magnetic surveys during the past 50 years are reviewed here. The prime factor was the development of the airborne magnetometer. Its application quickly showed the value of magnetic maps as aids in geologic mapping and in determining basement structure. Developments have included new types of magnetometers with greater sensitivity, and magnetic gradiometers, combined with the use of digital recording and processing routines. The worldwide coverage available is stimulating the preparation of magnetic maps on a continental scale for tectonic studies.