The precautionary concept has become intrinsic to international environmental policy, especially with the adoption, in 1992, of the Rio Declaration at UNCED. Principle 15 of that Declaration provides that: In order to protect the environment, the precautionary approach shall be widely applied by States according to their capabilities. Where there are threats of serious or irreversible damage, lack of full scientific certainty shall not be used as a reason for postponing cost-effective measures to prevent environmental degradation. The challenge facing the international community is how to attain truly precautionary environmental policies. This challenge is one of changing perceptions as much as of changing institutions or technical mechanisms. It is a challenge to our way of viewing the world as much as to our views of the role of science, or the burden of proof. It also raises a question as to the role of legal and other regulatory instruments in implementing the precautionary principle. This question, however, lends itself to a multifaceted and multidisciplinary approach.