The diagnosis of allergic diseases depends first and foremost on a careful medical history taken by a suitably experienced clinician. An allergy history concentrates on the relationship between the consistency of the patient’s problems with allergic diseases and the likelihood that the problems are the result of allergen exposure. The clinical suspicion of allergic disease is enhanced when the patient demonstrates IgE specific for the allergen or allergens identified by the history. Ultimately, the diagnosis is confirmed by the patient’s response to allergen avoidance or other therapeutic trials. Both skin tests and blood tests for allergen-specific IgE can be very useful in diagnosis when the strengths and limitations of each are understood and appropriately used by the clinician.