The ocean is becoming more acidic worldwide as a result of increasing atmospheric concentrations of carbon dioxide (“CO2”) and other pollutants. This fundamental change is likely to have substantial ecological and economic consequences globally. In this Article, we provide a toolbox for understanding and addressing the drivers of ocean acidification. We begin with an overview of the relevant science, highlighting known causes of chemical change in the coastal ocean. Because of the difficulties associated with controlling diffuse atmospheric pollutants such as CO2, we then focus on controlling smaller-scale agents of acidification, discussing ten legal and policy tools that state government agencies can use to mitigate the problem. This bottom-up approach does not solve the global CO2 problem, but instead offers a more immediate means of addressing the challenges of a rapidly changing ocean. States have ample legal authority to address many of the causes of ocean acidification; what remains is to implement that authority to safeguard our iconic coastal resources.