This chapter focuses on the ozone layer present in the lower stratosphere and its biological significance. The ozone is created and destroyed by ultraviolet radiation from the sun. Various natural phenomena, such as volcanic eruptions and the emmission of chemicals such as chlorofluorocarbons (CFCs), also disturb the ozone layer, resulting in an ozone hole. A decline in stratosphere ozone levels increase terrestrial ultraviolet radiation. The chapter also explores ultraviolet radiation and its biological effects and its effects on agricultural yields, the eco-system, and amphibian species. Ultraviolet light promotes a synthesis of vitamin D, which has a beneficial effect on human health. The mechanisms of all the other effects, which are negative and lead to cortical cataracts, skin cancer, melanoma, and sunburn; DNA damage and photo-immunosuppression; are also described. DNA repair systems, photo-reactivation, and photolysis, the effectiveness of sunscreens, suntan, and solaria are also detailed.