Urticaria is one of the most common diseases in dermatology and allergy. Unlike many other diseases, the ? eeting nature of the wheals makes ? rst diagnosis by both patients and phy- cians in many cases easy. However, this only refers to the ordinary wheals. The disease itself is highly complex in nature, with variety of clinical manifestations ranging from pinpoi- sized wheals to extensive angiodema. Complexity is also seen in the diversity of possible eliciting factors, the many different clinical subtypes and the therapeutic responsiveness. Only in recent years has a better understanding of the diversity in the different subtypes led to new classi? cations and new evidence-based guidelines for diagnostics and mana- ment of the disease. While mast cells are in the center of most urticaria reactions, it is now clearly understood that the responsible mediators are not only limited to histamines. The current book appears in a series of books by Springer. In 1986, the ? rst monograph was edited by Professor Henz nee Chanewsky. Since then, two updates of the book have appeared in the German language with Professor Henz as ? rst editor and T. Zuberbier, J. Grabbe, and E. Monroe as the co-editors of the most recent English version, published in 1998. All these books have been written as a joint effort of Professor Henz together with her team at the Department of Dermatology at the Virchow Clinic, Humboldt University, Berlin.