Previously perceived as an anomaly, eosinophilic esophagitis is now frequently diagnosed by both pediatric and adult specialists including gastroenterologists, allergists, pathologists, and otolaryngologists. Research efforts initially focused on characterization of the clinical, endoscopic, and histologic features of this disorder. In the last 3 years, the research focus has evolved into understanding its immunologic and demographic features as well as the development of efficacious therapies.Population-based demographic studies have documented the unique epidemiologic parameters of eosinophilic esophagitis, some of its natural history, and its increasing frequency. Basic research efforts have identified cytokines relevant toward development of eosinophilic esophagitis, including interleukin-5 and interleukin-13. Clinical efforts have established the efficacy of dietary and medical treatments. Some treatments result in symptomatic improvement with ongoing inflammation, so a debate is ensuing over the long-term effect of asymptomatic esophageal inflammation.Understanding of eosinophilic esophagitis has evolved to a point at which patients can be appropriately diagnosed and initially treated; however, a paucity of long-term outcome data prevents the creation of uniform recommendations for the clinical care of patients with eosinophilic esophagitis.