A design concept and the performance characteristics for a fusion transmutation of waste reactor (FTWR), a subcritical fast reactor driven by a tokamak fusion neutron source, are presented. The present design concept is based on nuclear, processing, and fusion technologies that either exist or are at an advanced stage of development and on the existing tokamak plasma physics database. An FTWR, operating with keff 0.95 at a thermal power output of ~3 GW and with a fusion neutron source operating at Qp = 1.5 to 2, could fission the transuranic content of ~100 metric tons of spent nuclear fuel per full-power year and would be self-sufficient in both electricity and tritium production. In equilibrium, a nuclear fleet consisting of light water reactors (LWRs) and FTWRs in the electrical power ratio of 3/1 would reduce by 99.4% the actinides discharged into the waste stream from the LWRs in a once-through fuel cycle that must be stored in high-level waste repositories.