The combination of spacecraft electrical power and on-board propulsion can consume as much as three-fourths of the mass of a spacecraft depending upon the mission. With the current emphasis on reducing costs (including launch vehicle costs) and on reducing the mass of future spacecraft it is apparent that the use of advanced spacecraft electrical power and on-board propulsion technologies must be employed. Some of the NASA-sponsored and other-sponsored technologies are examined showing how existing advanced power and propulsion technologies can be used to improve the performance of spacecraft. The synergistic effect of applying both advanced electrical power and advanced on-board propulsion technologies is specifically discussed.