The technical basis of environmental regulation is always at the edge of scientific and engineering understanding. As knowledge improves, questions will inevitably arise about past decisions. Understanding how the regulatory system accommodates changing scientific and engineering knowledge is vital for achieving environmental values. In this new volume, seven case studies shed light on the interplay between environmental regulation and scientific and engineering understanding, with practical conclusions on how science and engineering should be used for more sound and timely regulatory decision making. The book provides helpful timelines of scientific and regulatory developments for the cases, which include: factors impeding clean-up strategies in the Chesapeake Bay; pivotal questions in the regulation of ambient ozone concentrations; how science has been heeded but also ignored in regulation of new municipal waste combustors; impact of scientific findings on control of chlorination by-products; acid rain and what can be learned about research and public policy debate; controversy over the need for formaldehyde regulation; and the effect of public perception on management decisions concerning dioxin. This volume will be of practical interest to policymakers, business and environmental advocates, scientists, engineers, researchers, attorneys, faculty, and students.