Critical ITER physics requirements and R&D issues are considered and, the relevance and capability of JET in investigating these issues are discussed. In particular, JET gives its highest priority to a coherent programme in support of the design of an ITER divertor operating in a regime consistent with a small scrape-off length. JET intends to perform critical tests of such divertor regimes in D/T plasmas. Initial results from JET after its extensive modifications are presented. These show that the new divertor in JET has good power handling capability and carbon blooms, that often plagued the earlier campaign of high performance, have not yet been observed. Good progress in divertor characterisation and, in achieving the H, VH-modes and full LHCD non-inductive current drive has been made. Also, a valuable insight into the ELM behaviour and their occurrence is being gained.