Previously believed a rare condition, there has been a rising number of cases of eosinophilic esophagitis in adult and pediatric populations over the past several years. Because of this increase, it is important for clinicians to be able to recognize, diagnose, and manage this disease. This article focuses on the history and nomenclature of eosinophilic esophagitis and its evolution as a separate entity from gastroesophageal reflux disease. It also outlines currently accepted diagnostic criteria for this increasingly common condition.