The JET Programme in Support of ITER has entered its second phase, in which the boundaries for safe plasma operation with an ITER-like Wall are being explored. A key element of these studies is the benchmarking of the codes that are being used for ITER to predict plasma-wall interactions and, more generally, the influence of wall material on plasma performance and regimes of operation. Studies have focused on material migration and erosion, disruptions and runaway electron beams, and optimisation of plasma and divertor performance. In addition, a dedicated tungsten divertor melt experiment was carried out and provided key information for the ITER decision to begin operation with an all-W divertor. Initial results underline the strong influence that the wall material has on plasma performance and regimes of operation but show that there is significant scope for optimisation by careful discharge design. The future JET programme will concentrate on completing this optimisation and demonstrating the resulting performance in deuterium-tritium plasmas, thus providing the best possible preparation of ITER operation.