Food allergy gathers the bulk of pathologies linked to the immuno-allergic response to various foods. It is most often due to an IgE-dependent mechanism. Food allergy may be expressed by various clinical pictures: atopic dermatitis, asthma, anaphylactic shock, urticaria. Its actual incidence is probably underestimated. Diagnosis rests on logical and rigorous advance of thought based on history, physical examination and dietary inquiries. Skin prick-tests constitute the choice method for searching sensitization towards food allergens. Biological assays directed towards specific IgE are second-intention tests. Oral provocation tests constitute the gold standard for establishing the role of a food in the appearance of symptoms. They should be conducted under close medical supervision. Eviction-reintroduction methods represent a heavy diagnostic approach, with rare indications at the present time. The strictness of the methodology used by the allergologist is essential for establishing the diagnosis of food allergy.