Blowfly infestation of traditionally processed fish is a serious problem that results in significant physical and economic losses. It also leads to the unregulated use of inappropriate and hazardous insecticides by fish processors in some developing countries. This manual provides guidance on the biology of blowfly infestation and its control. Emphasis is placed on the recently developed systems based approach to controlling infestation, which engages the fish processor in identifying those steps in the process where infestation occurs and selecting appropriate control measures.