To meet the requirements of the scientific programme, the EFDA JET Real Time Measurement and Control Project has developed an integrated set of real-time plasma measurements, experiment control, and communication facilities. Traditional experiments collected instrument data during the plasma pulse and calculated physics data after the pulse. The challenge for continuous tokamak operation is to calculate the physics data in real-time, keeping up with the evolution of the plasma. In JET, many Plasma Diagnostics have been augmented with extra data acquisition and signal-processing systems so that they can both capture instrument data for conventional post-pulse analysis and calculate calibrated, validated physics results in real-time. During the pulse, the systems send sampled data sets into a network, which distributes the data to several destinations. These may do further analysis integrating data from several measurements or may control the plasma scenario by heating or fuelling. The simplest real-time Diagnostic systems apply scale factors to the signals, as with the Electron Cyclotron Emission Diagnostic's 96 tuned radiometer channels, giving the electron temperature profile. In various Spectroscopy Diagnostics, spectral features are least-squares-fitted to measured spectra from several lines of site, within 50ms. Ion temperatures and rotation speed can be calculated from the line widths and shifts. For Diagnostics using modulation techniques, the systems implement digital-signal processing phase trackers, lock-in amplifiers and filters. The interferometer samples 15 channels at 400kHz for 30 s, i.e. 6 million samples/sec! Diagnostics have specific lines of sight, spatial channels and various sampling rates. The Heating/Fuelling systems have relatively coarse spatial localisation. Analysis systems have been developed to integrate the basic physics data into smaller sets of controllable parameters on a common geometry e.g. temperature, density and safety factor profiles with values at 10 points of normalised radius. The EFDA Real Time project is essential groundwork for future reactors such as ITER, and has successfully involved many scientific and technical staff from several institutions. The facility is now frequently used in experiments. This work has been conducted under the European Fusion Development Agreement and is partly funded by Euratom and the UK Engineering and Physical Sciences Research Council.