High power fast waves are routinely used in Tokamaks either in the Ion Cyclotron Resonance Heating (ICRH) regime or, by adjusting the frequency to avoid this powerful resonance, in the electron damping regime (Landau and Transient Time magnetic pumping). ICRH is a well established method for plasma heating in a variety of plasma conditions. These include high performance plasmas such as H-modes in JET[l] and ASDEX [2], high βP VH modes in JET [3] and shear reversal configurations produced by pellet enhanced H-modes in JET [4] The data base on fast wave electron and ion current drive has expanded rapidly during the last five years. Electron current drive by a combination of transit time magnetic pumping and electron Landau damping is now a proven method [5,6,7,8] for driving current in the plasma centre (DIII-D, Tore Supra, TFTR) while minority ion current drive has been successfully employed on JET to change the current density gradient at the q= l surface and control the sawtooth period [9]. These heating and current drive experiments have formed the basis to support ICRH as one of the main candidate methods for additional heating on ITER. In addition, when RF waves are damped on minority species, or on majority species at harmonics of the ion cyclotron frequency, a large population of well confined fast ions whose energy can extend up to a few MeV, can be created. They constitute the closest way to simulate the behaviour of alpha particles in reactor type devices. This paper presents ICRH physics aspects mostly related to this simulation.