Food allergic reactions have generated increasing concern in the United States, with approximately one fourth of American households altering their dietary habits because a member of the family is perceived to suffer from food allergies. IgE-mediated (type I) hypersensitivity accounts for most well-characterized food allergic reactions, although non–IgE-mediated immune mechanisms are believed to be responsible for a variety of hypersensitivity disorders. This article examines adverse food reactions that are IgE-mediated, non–IgE-mediated, and those entities that have characteristics of both.