Editors' Summary: The role of science and law are often at a cross-roads in the world of environmental policymaking. The law imposes legal norms based on what has been generally accepted in scientific circles. In turn, scientific claims are accepted only if they satisfy evidentiary rules prescribed by the law. One may be tempted to postpone decisions until we have all the pertinent scientific evidence before us. But failing to act can be costly--both in terms of financial resources for additional research and of environmental ills that persist while we delay decisions. We must therefore tolerate some degree of uncertainty. But while we may not agree with the decisions, we should know how and why they were made despite the limitations of scientific knowledge. Using a "Bayesian approach," the author demonstrates how policymakers can transparently acknowledge their theoretical and empirical limitations and can communicate the effects of choices they make in certainty's absence.