This article, the first of a series of three on the GEM program to appear in Eos, provides an overview of the program organization and current scientific activities. The second article by George Siscoe will report on GGCM development, and the third article by Larry Lyons will report on the GEM observing campaigns and data/model comparisons.The Geospace Environment Modeling (GEM) Program is now in its third year as one of the U.S. global change programs receiving core support from the Geosciences Directorate of the National Science Foundation. The GEM program is contributing to progress in space environment forecasting and to the fundamental understanding of geospace in general by enabling the construction of a Geospace General Circulation Model (GGCM) with predictive capabilities. The observational component of the program provides for the deployment and intercalibration of a worldwide network of ground‐based instruments that are used to monitor the dynamical state of the magnetosphere and ionosphere, as well as statistical trends in their variations. Because the scope of both the modeling and observing efforts are ambitious and global, GEM participants are making use of resources within both the U.S. and international space and atmospheric science communities that effectively leverage the modest resources that are currently available for the program from NSF.