It is possible, through nuclear reactions, to transmute long-lived radionuclides into shorter-lived or stable nuclides. Much attention has recently been focused on approaches to transmutation of spent nuclear fuel and on the potential benefits and risks of transmutation. Drawing on findings from studies carried out in different countries, this paper assesses the potential impacts of transmutation in standard thermal and fast reactors. A parametric scoping using standard methods to analyze mass flows and waste hazards gives a sense of the limitations and key variables in transmutation. With respect to waste, the impacts of the transmutation effort are found to depend strongly on the separation efficiency of the reprocessing system, the performance of the disposal repository, and the transmutation rate in the reactor.