This issue of Immunology and Allergy Clinics of North America, Guest Edited by Anne Marie Ditto, MD, is devoted to Anaphylaxis. Dr. Ditto has assembled a group of expert authors to review the following topics: Idiopathic Anaphylaxis; Mast Cell Activation Syndromes Presenting as Anaphylaxis; Anaphylaxis to Chemotherapy and Biologics; Fatal and Near Fatal Anaphylaxis; Anaphylaxis to Drugs; Perioperative Anaphylaxis; Exercise-Induced Anaphylaxis; Anaphylaxis to Carbohydrate Side Chains-alpha -gal; Anaphylaxis to Food; Anaphylaxis to Insect Stings; and Treatment and Prevention of Anaphylaxis.