Geomagnetic field observations at the earth's surface are of interest to a variety of geophysicists and characteristically contain effects due to currents in the regions above the surface. A symposium on this subject was held during the April 16–20, 1973 meeting of the AGU and was cosponsored by the sections of Geomagnetism and Paleomagnetism and Solar-Planetary Relationships-Magnetospheric Physics. The program contained invited and contributed papers on the basic physics involved, the configuration of the sources, and the local time variations. The subsequent four papers represent some highlights from the invited reviews given by the authors. This introduction is intended to give some additional background on the geomagnetic field.