This Article presents the scientific basis for an effective acid rain control policy. Part I suggests that if a choice must be made, regulation should focus primarily on sulfur dioxide emissions rather than nitrogen oxide emissions because sulfur deposition is the major cause of watershed acidification. Part II explains the need for at least a fifty percent reduction in sulfur dioxide emissions to meet a safe deposition level. Part III specifies the geographical allocation of sulfur emission reductions necessary to attain target deposition levels in the northeastern United States and southeastern Canada. The Article concludes by demonstrating the need for swift adoption and implementation of an effective acid deposition control strategy i...