Despite their promise for major environmental and resource conservation benefits, electric vehicles to date have failed to capture significant applications, primarily because of the limitations of lead acid and nickel cadmium batteries. Emerging advanced batteries with high specific energy and fuel cells with high power density are now increasing the prospects for competitiveness of electric vehicles. Polymer electrolytes are playing important roles in these developments. The invention of polymer electrolytes is enabling the safe use of metallic lithium in batteries. Prototypical lithium polymer batteries using metal oxide positives capable of reversibly accepting lithium ions are achieving specific energies that meet the targets for electric vehicle application, and the emergence of cell technologies in which Lithium metal is coupled with polymer electrolytes and active sulfur positives is holding out promise for yet higher specific energies. Polymer electrolyte membrane (PEM) fuel cell technology is particularly well suited for mobile applications. A decade of R&D to maximize the three-phase boundary area between catalyst/conductor, polymer electrolyte and reactant gases has increased PEM fuel cell catalyst utilization and power density to levels acceptable for electric vehicle propulsion. The emphasis in battery and fuel cell polymer electrolyte development is now shifting to electrolyte, cell and module/stack manufacturing development and cost reduction, but continued research to understand and enhance bulk and interface properties of polymer electrolytes is likely to have significant practical payoff on the way to broadly competitive electric vehicles. (C) 2000 Elsevier Science B.V. All rights reserved.