The Northrop Grumman Avionics Simulation (AVSIM) is one of a set of simulations focused on fighter class radars. It is designed to support a variety of analysis and development activities, spanning requirements analysis, radar software development, performance evaluation, and pilot interfaces. This paper describes AVSIM and the simulation architecture that surrounds it. The model provides high fidelity representations of both Air-to-Air and Air-to-Ground radar modes, encompassing detection capability, measurement errors, tracking performance, and timelines. Analytical models are used to represent high data rate signal processing functions, while operational software is used for less intensive data processing such as radar control and tracking activities. AVSIM can be driven by models such as the Joint Integrated Mission Model (JIMM), or by tightly controlled scenarios from its own Scenario Generator. It can be run in real time as part of a cockpit simulator, or in Monte Carlo mode for detailed performance analysis. Extensive post processing capabilities provide insight into radar detection, measurement errors, tracking, and time-line performance. Scan patterns are also visualized, via playback capabilities. AVSIM represents a substantial advance in the state of the art for high fidelity multi-use avionics simulations.