<b><i>Background:</i></b> Eosinophilic esophagitis (EoE) is a chronic inflammatory disease of the esophagus associated with dysphagia in adults and refractory reflux syndromes in children. <b><i>Methods:</i></b> Immunological and genetic approaches have been used to better understand the pathophysiology of the underlying inflammation. <b><i>Results and Conclusions:</i></b> Evidence has accumulated that EoE represents a T-helper (Th) 2-type inflammatory disease, in which allergens play a role in triggering the disease. The majority of the patients suffer from concurrent allergic rhinitis, asthma, and eczema, and have a history of atopy. The chronic inflammatory response in EoE is associated with tissue damage and remodeling, both of which lead to esophageal dysfunction and bolus impaction. The new insights into the pathophysiology have resulted in the development of the first pharmacological therapies of EoE.