Anaphylaxis is an acute, systemic reaction mediated by immunoglobulin E hypersensitivity. Release of bioactive factors causes vasodilation and bronchiole constriction that can lead to hypotensive shock and asphyxiation. Differential diagnosis includes acute asthma, localized angioedema, syncope, and anxiety/panic attacks. Diagnostic tests lack specificity. Clinical diagnosis is based on demonstration of specific airway or cardiovascular compromise within proximity of allergen exposure. Treatment includes epinephrine, antihistamines, fluid resuscitation, and airway management. Prevention focuses on awareness/avoidance of triggers, implementation of personalized action plans, as well as immune modulation by desensitization in a closely controlled setting where available.