The skin, uniquely positioned at the interface between the human body and the external world, plays a multifaceted role in the expression of cancer. Primary skin cancer is the most common cancer afflicting mankind and is rising in inci dence, despite the fact that it is often preventable. Besides primary cancer, the skin may show direct and indirect evidence of internal cancer, thus serving as a window to the body for both laymen and physicians alike. In addition, the acces sibility of the skin is useful for the study of carcinogenesis as well as cancer treat ment options. lowe much of my interest in skin cancer to Dr. Leon Goldman, the father of dermatologic laser surgery, and to Dr. Edmund Klein, the father of modern immunotherapy. We, at the Roswell Park Memorial Institute, were indeed for tunate to have a wealth of patients available for study. Many of the illustrations used in this book were of my patients at the Institute, and I kindly thank the fol lowing publications and their respective publishers for allowing me to reuse some of my photographs, most notably: Cancer Medicine (2nd edition), Journal of Surgical Oncology, Journal of the American Academy of Dermatology, Archives of Dermatology, Cancer, and Journal of Dermatologic Surgery and Oncology. We are very fortunate in this work to have some of the world's foremost authorities in their areas as contributors, such as Drs. Zackheim, Lambert, J.W. Trimble, J.R. Trimble, Jackson, Crutcher, Mashberg, Wick, Sidell, F. Helm, G.