AbstractCritical 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 that carbon blooms, which often plagued the earlier campaign of high performance, have not yet been observed. Good progress in divertor characterization and, in achieving the H and VH modes and full lower hybrid non-inductive current drive has been made. Also, valuable insight into edge localized mode behaviour and their occurrence is being gained.