The American Geophysical Union has to do with those theoretical and applied sciences relating to the Earth, its configuration, its structure, and the natural forces acting upon and within it. Since the founding of the Union in 1919, it has gradually developed so that in 1952, with nearly 5000 members, it is perhaps the principal organization in the United States of America acting as a clearing house for new scientific thoughts and ideas relating to Geophysics.Sponsored by the National Research Council of the National Academy of Sciences, the Executive Committee of the Union is the Committee on Geophysics of the Council and the National Committee for the United States of America of the International Union of Geodesy and Geophysics.The wide-spread special interests of the eight Sections of the Union are expressed in papers presented at the annual meetings, in the regional meetings (often held in cooperation with other scientific organizations), and in the Union's Transactions, which were formerly published annually and published bimonthly since 1945. Symposia on timely subjects are annual features of the General AssembliesThe fields of the Sections of the Union are: (a) Geodesy; (b) Seismology; (c) Meteorology; (d) Terrestrial Magnetism and Electricity; (e) Oceanography; (f) Volcanology; (g) Hydrology; and (h) Tectonophysics.The American Geophysical Union has made every endeavor in the past 33 years to increase coordination and collaboration of interests, both nationally and internationally, and to maintain continuity of the functions of the International Union of Geodesy and Geophysics, thus protecting for future international activities those relations so essential to geophysical investigations, especially during World War II. A prominent Geophysicist of California has said: “The Union, in my opinion, is to be congratulated for having the vision and courage to proceed (during the War) with the annual meetings. The Nation needs more, not less, scientific endeavor.”In these chaotic days following World War II, as never before, responsibility for continued attainment of geophysical knowledge falls with particular emphasis upon the Geophysicists of the Western Hemisphere. Now, as never before, American scientists personally benefit by affiliation with their fellow scientists and co-workers, since the individual worker is under a great handicap. Now, as never before, scientists in general of the Western Hemisphere need to affiliate and play their part not only in the immediate problems of application, in which the Geophysicist is contributing effectively, but in the rehabilitation of international relations and endeavors particularly vital to investigations of the Earth sciences.This article must be limited to a general account of the origin and development of the Union during the 33 years from 1919 to June, 1952. As a matter of record, detailed particulars of the Union's history are given in the Appendices on subjects as indicated in the Table of Contents.