Acknowledging urticaria as a symptom of mast cell degranulation is stressed. The biology of the mast cell, and the recognized immunologic and non-immunologic mast cell secretagogues are individually discussed along with mechanisms of activation and mediators released. The major, preformed mediator histamine in the skin produces a prototypic, short-lived urticaria, however, the clinical spectrum and pattern of "hives" indicate that other mediators contribute to the polymorphism and variable behavior of this symptom. The clinical assessment is almost exclusively restricted to the history and physical examination. Features to review and examine are presented. The cause of "acute" urticaria is identifiable (by history) in the majority of patients, and except for hives that accompany an anaphylactic reaction, these patients rarely present to the physician for care. The persistent, or "chronic" hiver whose history cannot elicit a cause, is rarely triggered by an individual trigger, despite extensive professional evaluation. Evidence to support changing the chronological, "acute" and "chronic" classification of urticaria to "identifiable" and "non-identifiable" triggered urticaria is discussed, as is the futility of extensive, costly laboratory work-ups. The natural history of urticaria reveals that management should be directed toward allowing the patient to maintain an acceptable quality of life (with or without some urticaria), until the episode resolves.