The molecular events resulting in melanocyte transformation and the development of early melanoma are incompletely understood. Risk factors for the development of melanoma include genetic, phenotypic and environmental risk factors and can overlap. Also, persons with large numbers of nevi face a higher risk of melanoma. These risk associations, combined with knowledge obtained from basic studies on the survival, differentiation, and proliferation of the melanocyte, can provide hints about the molecular mechanisms that underlie the development of nevi and melanoma.