JET has been operating for one year. The diagnostic capability has been progressively increased from the barely adequate initial level to the point where physics data on the internal plasma processes is available. The plasma current has been taken up to just over 3MA with flat-top times of several seconds. Central electron temperatures are in the range 1­3keV, mean electron densities (n) from 0.1­2.5¥l019m­3 and the derived global energy confinement tE reaches 0. 35s±30%. The radiation loss is substantial, ranging from 60­100% of the input power. The contamination of the plasma is high, giving typical values of Zeff ~5, limiting the maximum density, giving higher temperatures and lower <ntE> products than expected. Experiments and machine changes are in hand to overcome this problem.