This review examines the current state of the art in GAM technology and applications. It outlines the fundamental principles and discusses the benefits and limitations of the process. It describes the choice of equipment, including aspects such as nitrogen gas preparation and the position and timing of gas injection. The report also provides design guidelines for thin and thick section mouldings and the c258 and location of gas channels. External gas moulding is also briefly described. An additional indexed section containing several hundred abstracts from the Rapra Polymer Library database provides useful references for further reading.