An integral component of the multi-agency U.S. Global Change Research Program (Our Changing Planet," Committee on Earth Sciences, 1991) is understanding and modeling the geospace environment. As part of its contribution to the U.S. Global Change Research Program, the National Science Foundation's Division of Atmospheric Sciences has established a new research initiative, Geospace Environment Modeling (GEM), with the goal of supporting basic research into the dynamical and structural properties of geospace, leading to the construction of a global geospace model with predictive capability. The subjects of the first GEM campaign are the magnetospheric boundary, the magnetosheath beyond it, and the connection from the boundary through the magnetosphere to the ionosphere. This grant is for support to model electron and ion distribution functions near and within the dayside magnetopause in order to identify key particle signatures of the magnetopause electric and magnetic fields. The codes prepared for this project will be made available for inclusion into the GEM program's Global Circulation Model.