An international agreement known as the Montreal Protocol on Substances That Deplete the Ozone Layer was reached in 1987. Through that agreement and its subsequent amendments and adjustments, many nations of the world have carried out policies to reduce and then phase out their use of ozone-depleting chemicals. The Montreal Protocol also called for the international scientific community to periodically update governments on the latest scientific findings related to the ozone layer. Conducted under the auspices of the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) and co-sponsored by NASA, NOAA, and the European Commission, these periodic "state-of-the-science" assessments have guided policymakers as they strengthened the original provisions of the Montreal Protocol. Together with colleagues at NASA, other NOAA laboratories, and other scientific institutions across the U.S. and around the world, CSL (formerly the Aeronomy Laboratory) has played a leading role in preparing these assessments (1985, 1988, 1991, 1994, 1998, 2002, 2006, 2010, 2014, 2018, and 2020).