Poly(methyl methacrylate) – so–called ‘acrylic resin’ – is usually the material of choice for full denture bases and ‘gumwork’ for removable devices. It has also been the chemical model for many other material developments in dentistry, such as restorative materials. The properties, behaviour and handling of poly(methyl methacrylate) likewise form a basis for understanding those other materials. A polymerization reaction is performed as part of the normal dental procedures in the laboratory, and the proper control of this is important for controlling the properties of the product. It is essential to understand both the heat-cured and cold-cured types, whose properties and limitations differ because of their processing differences.