AbstractSuccessful plasma heating is essential in present fusion experiments, for the demonstration of D-T burn in future devices and finally for the fusion reactor itself. This paper discusses the common heating systems with respect to their present performance and their applicability to future fusion devices. The comparative discussion is oriented to the various functions of heating, which are: •- plasma heating to fusion-relevant parameters and to ignition in future machines,•- non-inductive, steady-state current drive,•- plasma profile control,•- neutral gas breakdown and plasma build-up.In view of these different functions, the potential of neutral beam injection (NBI) and the various schemes of wave heating (ECRH, LH, ICRH and Alfvén wave heating) is analyzed in more detail. The analysis includes assessments of the present physical and technical state of these heating methods, and makes suggestions for future developments and about outstanding problems. Specific attention is given to the still critical problem of efficient current drive, especially with respect to further extrapolation towards an economically operating tokamak reactor. Remarks on issues such as reliability, maintenance and economy conclude this comparative overview on plasma heating systems.