The paper reports on ITER-relevant ICRF physics investigated on JET in 2003 and early 2004: minority heating of 3He and D in H plasmas, minority heating of tritium in D, investigations of finite Larmor radius effects on the RF-induced high-energy tails, and new results on the heating efficiency of ICRF antenna arrays. Studies of the ELMs using fast RF measurements, experimental demonstration of a new ELM-tolerant antenna matching scheme, and technical enhancements planned on the JET ICRF system for 2005, themselves likewise strongly driven by the preparation for ITER, are also summarized.