The Joint European Torus (JET) tokamak will ultimately have 15 MW of additional heating in the ion cyclotron range of frequencies (ICRF). Three uncooled prototype antennas and associated 3-MW generators are already operational and have coupled up to 6 MW to the plasma for pulse lengths up to several seconds. Eight cooled antennas for long-pulse operation are to be installed in 1987, and manufacture of these systems is well advanced. The design and development of the major components of this ICRF system — the radio-frequency (rf) generators, the coaxial transmission lines, the tuning facilities, and the antennas — are detailed. A test bed for rf testing of the components and assemblies has been installed on JET and test results are also presented. Underlying analytical studies of the various operating scenarios (3He or hydrogen minority heating, second harmonic heating, etc.) of the influence of the k‖ spectrum, and of modeling of the antennas to predict coupling resistance and impedance are also summarized. Preliminary results from the initial operation of the prototype antennas are presented.