AbstractThe ECRH system of ASDEX Upgrade is now completed. Four gyrotrons generate a total Gaussian beam power of 2 MW/2 s at 140 GHz. The power is transmitted partly quasioptically and partly via corrugated HE-11 waveguides. The transmission line losses, determined calorimetrically, are about 12%. The four focused beams lead to a very localised power deposition in the plasma and can be steered in both poloidal and toroidal directions.