ABSTRACTHigh power gyrotrons have been developed for application to plasma heating in the program of magnetically confined nuclear fusion research. Gyrotron power levels of up to 1 MW in long pulse operation (>ls) and up to 200 kW in true continuous operation (CW) have been demonstrated at frequencies in the 8 to 140 GHz range. The status of high power gyrotron development is reviewed. One current goal of the worldwide gyrotron effort is the development of 1 MW,CW gyrotrons at a frequency of about 170 GHz for heating the proposed international tokamak ITER to ignition. Gyrotrons are also now being used in a variety of other applications including materials processing. Improved gyrotrons with features such as wide range tuning could be developed for industrial applications.