Experiments on JET require reliable control of basic plasma variables such as density, temperature and reaction rate. The real-time power control system provides a significant advance in the control capabilities by deriving suitable plasma heating rates and gas introduction rates in real time based on diagnostic information from the plasma. The most innovative feature is to provide control room staff with a safe and easy method of defining control scenarios known as networks on-line. These networks can be tested immediately with data from previous pulses and then loaded for the next pulse. This paper presents details of the engineering design of the system.