This paper reviews adverse reactions to foods, which are defined as toxic (due to food contaminants that cause a reaction in any individual if the dose is high enough) and nontoxic reactions (immune-mediated (food allergies) and non-immune mediated (food intolerance)). The clinical manifestations of food allergy are described and examples of food intolerance, adverse reactions to food additives and other reactions that may be influence by dietary factors are given. Methods used to diagnose food allergy and the management of food allergy are also described.