Published Article / The paper presents a critical review of the techniques that are used to cool plastic injection moulds. It examines research on cooling of injection moulds by conventional cooling, the benefits and the limitations of the method. It compares the deployment mechanisms that have been proposed by various researchers. It also examines how the various mechanisms affect the plastic cooling rate and the overall heat transfer performance of the mould and how the various deployments affect the stress distribution of the mould and mould durability. The paper also presents the possibilities that have been presented by rapid prototyping. It discusses the development of conformal cooling as an alternative to conventional cooling. It presents the state of the art on the method. The paper presents the deficiencies in the current theories on conformal cooling and suggests areas that require further work in order to fully exploit the technique.