Peter A. Miescher The skin has always been one of the major targets to clinicians interested in immunology. Initially, the main focus was centred on allergic conditions such as contact hypersensitivity and urticeria. Gradually, the spectrum of immunological conditions involving the skin increased, encompassing diseases such as Dermatitis Herpetiformis, Erythema Muitiforme, Cutaneous Bullous Disorders and Photo- toxic Reactions. It has been the intention of the editors of Springer Seminars in Immu- nopathology to cover the broad spectrum of immune phenomena encountered in dermatological diseases with special emphasis to newer developments in Immunopathology. Dr. 1. N. Gigli has managed to assemble a series of important contributions within two issues of the Journal which are of such an interest to dermatologists that we decided to publish this topic as a separate volume for all dermatologists who do not have access to Seminars in Immunopathology. 3 Immunologically Mediated Epidermal Cell Injury Richard D. Sontheimer* and James N. Gilliam Division of Dermatology, University of Texas Health Science Center, 5323 Harry Hines Boulevard, Dallas, Texas 75235, USA Introduction The epidermis is a functional unit of different cell types that has the critical role of protecting man from his environment. The three major cell types that make up the epidermis (keratinocytes, melanocytes, and Langerhans cells) serve different protective functions. The vast majority of epidermal cells are keratinocytes (Fig. 1).