This resource describes the depletion of ozone in the upper atmosphere, which filters out incoming radiation in the cell-damaging ultraviolet (UV) part of the spectrum. Other topics include a detailed description of the chemical interaction between chlorofluorocarbons (CFCs) and ozone and a list of other ozone depleting chemicals. Information is also available on the ozone layer, ozone holes above Antarctica and the Arctic, the polar vortex, methods of measuring and monitoring ozone depletion and efforts to reverse the problem, including the Montreal Protocol.