Well-documented and clearly-written, this important volume examines the interaction between scientific and engineering knowldege and the exercise of policy discretion in environmental, health, and safety regulation. The findings presented in the work derive in large part from a three-year study of two regulatory programs, the hazardous air pollutant program of the Environmental Protection Agency and the occupational health standards program of the Occupational Safety and Health Administration, and are based upon the activities within these programs between 1971 and 1980. The author's first-hand experience in the Office of Science and Technology in the Executive Office of the President during the Carter Administration further enhances the authority and thoroughness of the volume.