Acrylonitrile–butadiene–styrene (ABS) polymers are composed of elastomer dispersed as a grafted particulate phase in a thermoplastic matrix of styrene and acrylonitrile copolymer (SAN). The presence of SAN grafted onto the elastomeric component, usually polybutadiene or a butadiene copolymer, compatabilizes the rubber with the SAN component. Property advantages provided by this graft terpolymer include excellent toughness, good dimensional stability, good processibility, and chemical resistance. The system is structurally complex. This allows considerable versatility in the tailoring of properties to meet specific product requirements. Consequently, research and development in ABS systems is active. Numerous grades of ABS are available, including new alloys and specialty grades for high heat, flaming-retardant, or static dissipative product requirements. Good chemical resistance combined with the relatively low water absorptivity (<1%) results in high resistance to staining agents. Antioxidants substantially improve oxidative stability. Applications involving extended outdoor exposure require the use of stabilizing additives, pigments, and protective coatings. In manufacturing, grafting is achieved by the free-radical copolymerization of styrene and acrylonitrile monomers. The commercial processes for manufacturing ABS are discussed. ABS can be processed by compression and injection molding, extrusion, calendering, and blow molding. Postprocessing operations include cold forming, painting, and adhesive bonding. ABS is one of the two major plastic materials used in 3D printing, an emerging additive manufacturing technology that is developing rapidly in the last couple of decades. As a ‘bridge’ polymer between commodity plastics and higher performance engineering thermoplastics, ABS has become the largest selling engineering thermoplastic.