The International Union of Geodesy and Geophysics (IUGG; French: Union géodésique et géophysique internationale, UGGI) is an international non-governmental organization dedicated to the scientific study of Earth and its space environment using geophysical and geodetic techniques. The IUGG is a member of the International Science Council (ISC), which is composed of international scholarly and scientific institutions and national academies of sciences.

The IUGG was established in Brussels, Belgium in 1919.

IUGG's objectives are the promotion and coordination of studies related to Earth's physical, chemical and mathematical representation. This includes geometrical shape, internal structure, gravity and magnetic fields, seismicity, volcanism, hydrologic cycle, glaciers, oceans, atmosphere, ionosphere, and magnetosphere of Earth. It also includes solar, lunar and planetary studies. Some areas within its scope are environmental preservation, reduction of the effects of natural hazards, and mineral resources.

The IUGG consists of eight semi-autonomous associations:

It has also established six commissions to promote interdisciplinary problems:

and the Union Working Group on History.

List of General Assemblies, Presidents, and Secretaries-General.