The layer-by-layer molecular-level manipulation of conjugated polyions has been successfully utilized to fabricate ultrathin multilayer films and multilayer heterostructures. Through a process involving the alternate spontaneous adsorption of oppositely charged polymers from dilute aqueous solutions, multilayer thin films were fabricated from a variety of different bilayer combinations including conjugated/nonconjugated polyion bilayers, conjugated/conjugated polyion bilayers, and precursor polymer/conjugated polyion bilayers. UV-vis absorbance measurements revealed that in all cases the bilayer deposition process was linear and highly reproducible from layer to layer. Kinetic studies showed that the equilibrium adsorption of a polyion layer is reached within about 10 min and the process can be carried out onto different substrate surfaces. The typical bilayer thickness ranges from approximately 10 to 25 Angstrom and can be readily controlled by variations in such parameters as solution concentration, pH, doping level, and ionic strength.