Definitions of the precautionary principle (PP) are reviewed with particular reference to the role of risk assessment. In general, the PP is employed as a means of justifying decisions that are contrary to the conclusions of a formal risk assessment. Even where risk assessment is accepted as part of a precautionary approach, its importance in subsequent decision-making tends to be undermined by application of the PP. The implications for the future of risk assessment-based decisions in areas as diverse as environmental protection and food safety are briefly considered.