After the most demanding operation period in the JET history with 3717 pulses and a Trace Tritium Experiment in 2003, a 12 months maintenance period started on 6th March 2004, aiming at reinforcing to the capability of JET to prepare ITER operation. The heating power will approach 40 MW, in particular with the installation of an ITER-like ICRH antenna. The geometry of the divertor will be modified to allow greater flexibility in plasma configurations, in particular in producing high-triangularity ITER-like scenarios at higher plasma current, i.e. closer to ITER plasma regimes. Finally, a new set of diagnostics will come into operation designed to address a number of crucial phenomena for ITER operation, from the physics of the power handling to the tritium retention.