Peanut allergy has become a major health concern worldwide, especially in developed countries. However, the reasons for this increasing prevalence over the past several decades are not well understood. Because of the potentially severe health consequences of peanut allergy, those suspected of having had an allergic reaction to peanuts deserve a thorough evaluation. All patients with peanut allergy should be given an emergency management plan, as well as epinephrine and antihistamines to have on hand at all times. Patients and families should be taught to recognise early allergic reactions to peanuts and how to implement appropriate peanut-avoidance strategies. It is imperative that severe, or potentially severe, reactions be treated promptly with intramuscular epinephrine and oral antihistamines. Patients who have had such a reaction should be kept under observation in a hospital emergency department or equivalent for up to 4 h because of the possible development of the late-phase allergic response. This Seminar looks at the changing epidemiology of this allergy--and theories as to the rise in prevalence, diagnosis, and management of the allergy, and potential new treatments and prevention strategies under development.