Superantigens constitute a growing family of bacterial and viral proteins that share the capacity of inducing massive activation of the immune system. This volume contains contributions from leaders in the field of classical T cell superantigens and sheds light on relevant B cell superantigens at the molecular and biochemical levels. Moreover, articles in this publication deal with the emerging, intriguing possibility that immunoglobulin superantigens can activate primary effector cells of allergic disorders both in vitro and in vivo, thus acting as superallergens. A detailed account is also given of the biochemical, immunological and clinical characteristics of several endogenous, viral and bacterial superallergens, which are probably relevant in a variety of human diseases. This is the first volume to put together basic and clinical aspects of the classical T cell superantigens, B cell superantigens and superallergens. It will therefore be indispensable reading to basic and clinical immunologists, microbiologists, virologists and specialists in allergic and immune disorders.