The incidence of sunlight-induced skin aging and skin cancers, particularly melanoma skin cancer, has been increasing in many parts of the world. Authorities are recommending primary prevention programs to reduce cutaneous photodamage and skin carcinogenesis. An integral component of these programs is the use of protective clothing and effective sunscreens. Most modern sunscreens have highly efficient absorption or reflecting capabilities throughout ultraviolet B, partly ultraviolet A, and in some instances infrared wavelengths. Over the last several years, more efficient sunscreening ingredients have been developed for improved skin protection. More recently, direct evidence has demonstrated the effectiveness of sunscreens in their ability to reduce the incidence of solar keratoses. This article reviews the protectiveness of sunscreens and assays that predict their levels of protection.