The ozone layer, located in the stratosphere and containing about 90% of atmospheric ozone molecules is a key feature of the atmosphere, as it protects life on Earth by filtering out damaging ultraviolet radiation from the sun. Despite its central role in the Earth's atmosphere, the ozone equilibrium is fragile. It is governed by complex chemical processes involving atmospheric compounds which are several orders of magnitude less abundant than ozone. First alarms on the ozone layer linked to increased levels of chlorine compounds in the stratosphere due to emissions of industrial products such as chlorofluorocarbons were raised in 1970s. The Montreal Protocol on Substances that Deplete the Ozone Layer was signed in 1987 after the discovery in the early 1980s of the ozone hole, a large ozone decrease of more than 50 % of its total content above Antarctica during the Austral Spring. This protocol regulates the ozone depleting substances (ODS), and inorganic halogen species originating from these substances in the stratosphere reached a peak in the late 1990s. Since then the ozone layer is on the mend. Full recovery of the ozone layer will take decades due to the long lifetime of ODS in the atmosphere. In addition to their impact on stratospheric ozone, ODS are strong greenhouse gases. The Montreal Protocol has thus helped protect climate and the Kigali Amendment signed in 2016 was designed to regulate ODS substitutes characterized by a strong global warming potential. The seminar will present the latest findings on the evolution of the ozone layer together with the impact of ozone depletion and ODS increase on climate. Most recent threats on the ozone layer recovery will also be emphasized.