In February 2000, the European Commission adopted a Communication on the precautionary principle. This states how the Commission intends to apply the principle and establishes guidelines for its application. The document is intended to inform discussions on international agreements. In particular, it provides a defense of European Union (EU) precautionary policies in case of trade disputes, for example, in case the EU is accused of imposing unfair trade barriers on exports of genetically-modified (GM) products from the United States under the rules of the World Trade Organisation. In the communication, the Commission emphasizes the scientific aspects of the precautionary principle, perhaps partly to counter claims from US officials that the EU's reluctance to accept GM imports is not based on science but is politically-motivated. However, a principle is by definition a moral guide to behavior. In other words, it is an ethic. The precautionary principle should be viewed as a complement to science, to be invoked when a lack of scientific evidence means that outcomes are uncertain. Any interpretation of this principle needs to place at least as much emphasis on its ethical and value-based aspects as on its scientific justification. The Commission's interpretation risks undermining the painstaking progress made among European Union member states in responding to public concern about GM crops and food by adopting increased precaution. This paper explores the balance between the scientific and ethical/value-based aspects of the precautionary principle as set out in the Commission's communication, to make the case that it is the ethical and value-based aspects rather than the scientific aspects of the guidelines that need strengthening.