Polyelectrolytes are charged, usually water-soluble polymers which may be handled and processed at ambient conditions using materials of very low toxicity. It has been known for many years that solutions of oppositely charged polymers form complexes through multiple electrostatic interactions. Although many applications have been proposed for these complexes, few have been realized since the complexes are intractable once formed. A technique for producing polyelectrolyte complexes as uniform ultrathin films, some with internal structuring, was described in the early 1990s. Since then, numerous morphologies, compositions, and applications derived from complexed multicomposite (many different materials) films have been explored.