This directed case study covers fundamental information about ocean acidification using relevant examples from general science news articles as well as data excerpted from scientific research. It was developed for general environmental science classes and beginning science majors in college; however, it could also be used in high school classes. The case is divided into three sections, each with a different focus. Part I introduces the topic of ocean acidification and provides an overview of ocean chemistry and the pH scale. Part II presents carbon dioxide emissions and pH data for students to analyze. The data include historical estimations since the Industrial Revolution as well as recent emission projections from the past few decades. Part III examines the effects of ocean acidification on the shell of a marine snail, the sea butterfly (Limacina helicina). The case concludes with a broader consideration of the potential biological implications for other marine organisms and the environment in general.