The Precautionary Principle is a guide to coping with scientific uncertainties in the assessment and management of risks. In recent years, it has moved to the forefront of debates in policy and applied ethics, becoming a key normative tool in policy discussions in such diverse areas as medical and scientific research, health and safety regulation, environmental regulation, product development, international trade, and even judicial review. The principle has attracted critics who claim that it is fundamentally incoherent, too vague to guide (...) policy, and makes demands that are logically and scientifically impossible. In this paper we will answer these criticisms by formulating guidelines for its application that ensure its coherence as a useful normative guide in applied and policy ethics debates. We will also provide analyses of cases that demonstrate how our version of the principle functions in practice. (shrink)