A new type of thin-film electrode that does not utilize conducting polymers or traditional metal or chemical vapor deposition methods has been developed to create ultrathin flexible electrodes for fuel cells. Using the layer-by-layer (LbL) technique, carbon-polymer electrodes have been assembled from polyelectrolytes and stable carbon colloidal dispersions. Thin-film LbL polyelectrolyte-carbon electrodes (LPCEs) have been successfully assembled atop both metallic and non-metallic, porous and their non-porous substrates. These electrodes exhibit hi h electronic conductivities of 2-4 S cm(-1) and their porous structure provides ionic conductivities in the range of 10(-4) to 10(-3) S cm(-1). The electrodes show remarkable stability towards oxidizing, acidic, or delaminating basic solutions. In particular, an LPCE consisting of poly(diallyldimethyl ammonium chloride)/polv(2-acrylamido-2methyl- I -propane sulfonic acid)/carbon-platinum assembled on a porous stainless steel support yields an open-circuit potential similar to that of a pure platinum electrode. With LbL carbon-polymer electrodes, the membrane-electrode assembly (MEA) in a fuel cell can be made several times thinner, assume multiple geometries, and hence be more compact. The mechanism for LPCE deposition, electrode structure, and miniaturization will be presented and discussed, and demonstrations of the LbL electrodes in a traditional Nafion-based proton fuel cell and the first demonstration of a thin-film hydrogen-air "soft" fuel cell fully constructed using multilayer assembly are described.