The technology of the free electron maser (FEM) has advanced to where it now is an attractive source for electron cyclotron heating (ECH) in tokamaks at reasonable cost. FEM's are capable of producing CW power at frequencies 50–400 GHz with power levels up to 5 MW/module. They can operate as a high gain (30–40 db), wide band amplifier (Δf/f = 5–10%). Such systems incorporate high quality (low emittance and energy spread) electron beams of moderate current which are electrostatically accelerated before passing through a large amplitude wiggler. Highly efficient recovery of the energy from the “spent” beam is feasible and enhances the total FEM system energy to nearly 50% even though the beam extraction efficiency is rather modest.