JET is a large experimental Tokamak which has been constructed during the last 5 years by a European “Joint Undertaking” with the objective of studying the behaviour of plasma of a size and in conditions approaching those needed in a reactor. The experimental programme planned for 1983 — 1990, is based on a build-up of effective plasma heating to 10 MW of Neutral Beam plus 15 MW of R.F. power. Towards the end of this programme, D-T plasmas will be used, and the design and construction of the buildings and equipment incorporate suitable shielding and provision for remote-handling.