The Variable Specific Impulse Magnetoplasma Rocket (VASIMR) is described. As an open-ended, RF-heated, mirror-like plasma device, the system provides access to very high and variable plasma exhaust velocities of interest in high-speed interplanetary propulsion. The three-stage system is highly asymmetric and its value rests more in its capability as a power amplifier than as a plasma confinement device. During operation, a low-temperature, high-density plasma is generated in an injector which delivers it axially to a central heating stage. Once there, the flow is further heated to the desired conditions by ion cyclotron resonance techniques before exhausting it through a magnetic nozzle to provide modulated thrust. The system has been under study since 1980. At present, a multi-center theoretical and experimental program is under way, involving several research groups in the United States and which focuses on the development of the physics and engineering of these devices. This paper provides a status report of these activities, review the applicability of the technology, and examine new areas which should be addressed in the future.