Over recent years, human activities such as the burning of fossil fuels have increased the amount of carbon dioxide gas emitted to the atmosphere--and the amount that dissolves into the ocean. Now, so much carbon dioxide has been absorbed by the ocean that the chemistry of seawater is changing, causing the ocean to become more acidic. Based on a National Research Council report, this booklet describes the well-understood chemistry of ocean acidification and explores the many questions that remain: How will ocean acidification impact marine life such as fish, corals, and shellfish? How will the effects on individual species scale up to whole ecosystems? What will ocean acidification mean for aquaculture, the fishing industry, and coastal tourism?