The USU global ionospheric data assimilation model is part of the Global Assimilation of Ionospheric Measurements (GAIM). This model uses 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 that are assimilated include in situ electron density measurements from the DMSP satellites, bottomside electron density profiles from the Air Force network of digisondes, GPS-TEC data from a network of more than 900 stations, and occultation data. GAIM provides specifications and forecasts on a spatial grid that can be global, regional, or local. The primary GAIM output is in the form of 3-dimensional electron density distributions from 90 km to the geosynchronous altitude. GAIM also provides auxiliary parameters (NmF2, hmF2, NmE, hmE, slant and vertical TEC) and global distributions of the self-consistent ionospheric drivers (neutral winds and densities, electric fields, and particle precipitation). In its specification mode, GAIM provides quantitative estimates for the accuracy of the reconstructed ionospheric densities. In addition to the physics-based, Kalman filter model, we have also developed a Gauss-Markov Kalman filter model. The status of the models and the relevant applications are discussed.