Chronic urticaria has a spectrum of clinical presentations and causes. About 50% of patients with “idiopathic” disease have histamine-releasing autoantibodies in their blood. The term autoimmune urticaria is increasingly being accepted for this subgroup of patients, in whom immunosuppressive therapies may be appropriate if conventional approaches to management are unsuccessful. This article reviews the classification, causes, and management of chronic urticaria in light of recent advances in the understanding of its etiology. (J Am Acad Dermatol 2002;46:645-57.) Learning objective: At the conclusion of this learning activity, participants should have up-to-date knowledge of the classification, assessment, and management of chronic urticaria and understand where the concept of autoimmune urticaria fits into existing frameworks.