The ionosphere is a highly dynamic medium that can vary significantly from day to day and from hour to hour at a given location, and these variations can have detrimental effects on military and civilian systems. In an effort to minimize or circumvent the detrimental effects, a physics-based data assimilation model of the ionosphere and neutral upper atmosphere is under development with funding from the Multi-Disciplinary University Research Initiative (MURI) program. When completed, the GAIM model will provide specifications and forecasts on a spatial grid that can be global, regional, or local (25 km x 25 km). GAIM will use a physics-based ionosphere-plasmasphere-polar wind model and a Kalman filter as a basis for assimilating a diverse set of real-time (or near real-time) measurements. Some of the data to be assimilated include in situ electron density measurements from satellites, bottomside electron density profiles from ionosondes, Total Electron Content (TEC) measurements between ground-based receivers and the GPS satellites, occultation data from satellite constellations, and ultraviolet (UV) images of the upper atmosphere from imaging satellites. The resulting specifications and forecasts will be in the form of 3-dimensional electron density distributions from 90 to 25,000 km. In addition, GAIM will provide global distributions for the ionospheric drivers (neutral winds, electric fields, and particle precipitation), and in its specification mode, it will provide quantitative estimates for the accuracy of the reconstructed ionospheric densities. The current status of the GAIM program will be reviewed.