The introductory chapter briefly explores the initial motivation behind the aims of the precautionary principles, as well as some reasons why the precautionary approach to environmental risk management ultimately came under heavy scrutiny and became displaced by quantitative risk assessment as the dominant regulatory framework in the United States. The introduction highlights the contemporary debate over precautionary risk regulation, which is grounded in disagreement over how scientific uncertainty should shape environmental health policy. Specifically, critics of the precautionary principle maintain that in the absence of a preponderance of evidence to verify that exposure to a given effluent entails an actual risk to public health, we should refrain from restricting its use and emission, whereas proponents of precaution argue antithetically that in the absence of a preponderance of evidence to confirm that exposure to a given substance is safe to public health, we should preventatively safeguard the public against potential harm. The problem, however, is that both groups wrongly assume that their respective policy approaches alone can constitute an effective system of environmental risk management, and their diametrically opposed views would suggest that the choice between the precautionary principle and formal risk assessment is mutually exclusive. The introduction also details the plan of the book, foreshadowing the key arguments and objectives of each chapter.