Cutaneous lupus erythematosus (LE; syn LE-specific skin disease) is an autoimmune disease with well-defined skin manifestations often accentuated in a photodistribution and frequently associated with specific autoantibodies. These clinical observations have led to numerous laboratory studies related to the role of ultraviolet light, as well as studies of the cascade of immunologic events involved in the pathogenesis of cutaneous LE. We discuss the epidemiologic, clinical, and laboratory findings of cutaneous LE, including the classification of disease subsets. We review the evidence for abnormal photoreactivity in LE with an overview of the cellular, molecular, and genetic factors that may underlie this abnormality. As there is yet no convincing animal model of cutaneous LE, many studies remain descriptive in nature. To arrive at an understanding of the potential mechanisms underlying the development of cutaneous lupus, we discuss the role of ultraviolet light-mediated induction of apoptosis, antigen presentation, genetic factors, and mediators of inflammation. In addition, we consider the role and importance of humoral and cellular factors, synthesizing the current understanding of the pathophysiology of cutaneous lupus.