As a background for understanding the increased incidence of melanoma, relevant information focuses on incidence, morality, environmental factors, host factors, and genetic factors. Incidence has increased dramatically; however, it is not clear to what extent changes in behavior, in the environment, or in early detection are involved. The major environmental factor, ultraviolet radiation exposure, shows surprisingly modest risks for developing melanoma, approximately 1.7-fold, and so focus is turning to interactions of exposure with host factors, including genetic factors. The major host factors associated with the development of melanoma include skin type and numbers of nevi (as well as atypical nevi). Genetic factors associated with familial melanoma have been well described and new attention, not yet validated, is being paid to low penetrant genes and their polymorphisms.