The UKAEA-Euratom Association has now operated JET for the European Fusion Development Agreement for nearly five years, as the world-leading facility for ITER studies and featuring beryllium and tritium experience, fusion product detection and real time control of a reactor relevant plant. Developments continue in diagnostics, control, plasma heating systems and remote handling and many new systems are being installed as part of the Enhanced Performance up-grade. Facility operation requires machine protection systems based on sophisticated component analyses, to constrain operation within boundaries consistent with the desired plant life. Analyses show that life consumption of the key plant is ~10% at present, with operational limits of 4T, 5MA and 850t Vertical Disruption Event force.