UV radiation is a carcinogen known to play a role in the development of non-melanoma and melanoma skin cancers. Acute and chronic exposure to UV radiation causes clinical and biological effects that promote the unregulated proliferation of skin cells. In recent decades, changes in climate and increased air pollution have led to environmental changes that increase UV light transmission. In this chapter, we discuss sources of UV radiation that are relevant to human health, as well as the acute and chronic effects that result from UV radiation exposure.