The International Union of Geodesy and Geophysics (IUGG) was established in 1919 to promote activities of international scientific societies dealing with geodesy, terrestrial magnetism and electricity, meteorology, physical oceanography, seismology, volcanology, and hydrology. This paper first introduces IUGG, presenting its current structure, partners, and various activities before the origin and earlier development of the Union is described covering the period between the two World Wars.

Written for the centennial anniversary of the International Union of Geodesy and Geophysics (IUGG), this paper documents the activities of the Union at the beginning of the 21st century. IUGG added an eighth association on cryospheric sciences, introduced new categories of affiliate and honorary memberships, new grants, science education, and recognition programs, and formed new commissions on climatic and environmental change, data and information, planetary sciences, and history.