Ozone in the Earth’s stratosphere protects life from harmful ultraviolet radiation emitted by the sun. In the 1970s, scientists discovered that certain types of man-made chemicals could destroy stratospheric ozone. In 1987, countries adopted the Montreal Protocol on Substances that Deplete the Ozone Layer to address this threat. The Protocol has been strengthened through a series of formal amendments and other agreements. As a result, the production and use of ozone-depleting substances has been reduced significantly, and if progress continues the ozone layer should recover. Many policy-makers and scholars believe the ozone regime to be perhaps the most successful global environmental regime to date (see Chapter 9). At the same time, casual observers sometimes confuse the science of the issue with climate change (see Chapter 28), do not understand the regime’s basic history or key achievements, and are unaware of several problems that could prevent full recovery of the ozone layer.