A facility capable of direct synthesis of radar systems and their electromagnetic environments operating concurrently with missile flight simulations, range instrumentation sim ulations, and related test-range experiments has been needed for many years. This paper describes the design, development, and ap plication of a general-purpose Radar and Electromagnetic Environment Simulator operating under the combined control of digital and analog computers. This simulator is one of the more recent developments of the Analyses and Computation Directorate, White Sands Missile Range. In this system the combined operation of computers and microwave hardware is utilized to create realistic dynamic radio-frequency environmental effects based on time de lay, doppler shift, and RF-signal-power equations com bined with simulated radar and missile flight geometry dynamics and kinematics. Associated radar antenna pat terns, target backscatter patterns, clutter, and other target- induced RF phenomena are included. The simulator includes a flexible system for simulating RF signal generation and receiver signal-processing and provides a broad range of adjustment of radar parameters. The simulated transmitter signals are propagated through the computer-controlled environment simulation and are received and tracked by the receiver signal-processing equipment as in normal radar operations. Prototype radar subsystems and components, tracking beacons, jammers, counter-countermeasure receivers, and many other devices can be coupled into the simulator to be studied within the confines of the simulation laboratory.