This GESAMP study presents a set of objectives, goals, methodologies and a checklist for assessment and communication of environmental risks which may be associated with coastal aquaculture. It is structured to improve risk communication and to ensure that risk assessment is a scientific exercise in predicting environmental change. A set of six case studies is also presented to illustrate the use of the environmental risk assessment methodologies. These examples of environmental interactions span a range of cultured species from fin fish to molluscs and shrimp.