An overview is given of fusion relevant performance in a number of JET operational regimes. In most areas JET provides a suitable platform on which to base the design and predict the performance of a next step device. The main outstanding problem area is that of controlling impurity influxes and plasma exhaust, these are to be studied in a new phase programme under consideration for JET. The fusion performance already obtained in JET is described with 100 kW of fusion power being generated in charged particles from the D-He3 reaction and more than 10 MW of fusion power predicted from present discharges if operated in D-T.