The fact that technologies have unintended consequences is self-evident. But risk management - managing the adverse effects of technology - is both uncertain and politically contentious, since it entails making decisions about socially important issues in the face of scientific uncertainty. Originating in European environmental policy in the 1970s, the precautionary principle (PP) is embodied in adages such as "better safe than sorry" and "err on the side of caution". In practice, this means taking steps to avoid possible environmental or health damage, in the face of insufficient scientific evidence. The PP has achieved widespread political support, and - by the Treaty on European Union - it is the foundation of environmental policy in the European Union (EU). The PP is firmly established in international law, and a considerable body of case law is developing about its use in the EU. However, it has also generated immense controversy.