The presence of a compatibilizing agent permits the blending of otherwise incompatible polymers to yield polyblends or alloys with unique properties, generally not attainable from the individual components. Block and graft copolymers possessing segments with chemical structures or solubility parameters which are similar to those of the polymers being blended are effective compatibilizing agents. The latter may be preformed and added to the mixture of polymers undergoing compatibilization or may be generatedin situby reaction between coreactive functional groups on the polymers. The bonding between the segments in the compatibilizing agent, whether preformed or generatedin situ, is generally covalent, ionic, or hydrogen bonding. The compatibilizing agent acts as a polymeric surfactant, lowering surface tension and promoting interfacial adhesion between the dispersed and matrix polymer phases in a polyblend or alloy or between the layers in a laminate formed by extrusion or coextrusion. Numerous polyblends and laminates are discussed as illustrative of the concepts.