[en] The fusion reactor neutral beam program consists principally of development and application of positive ion based systems in the energy range of less than or equal to 120 keV. Reactor studies for both mirrors and tokamaks, and even studies of tokamak research devices beyond TFTR, indicate a need for higher energies and also higher efficiencies than can be obtained by extrapolating positive ion based systems. The relative merits of systems based on positive ions, positive ions with energy recovery, negative ions and negative ions with energy recovery are reviewed. Then the neutral beam system parameters called for by mirror and tokamak design studies are reviewed. It is found that although certain types of reactors require more efficiency than others, increased emphasis on the development of negative ions and direct recovery is prudent in any case, and that there should be a test of ripple assisted injection into a tokamak