Research from this laboratory on the sodium/solid polymer electrolyte (SPE) battery is described. Recent results show a performance level that equals or exceeds that of the better-known lithium analogs in terms of rate capability, cycle life and specific power, but at a lower projected cost per kilowatt hour, making sodium/SPE systems attractive for applications such as electric vehicles. Optimization of electrolyte composition and cathodes, using solid redox polymerization electrodes, sodium cobalt oxide or a new manganese oxide, is discussed, and areas for further study are suggested.