Stratospheric ozone depletion, driven by human-made chlorofluorocarbons (CFCs), is a major environmental issue of the 20th century. This review outlines the science and history of ozone depletion, focusing on chemical processes and evidence of depletion. Observations show that CFCs have caused about 10% depletion of stratospheric ozone near 40 km, with the most dramatic effects in Antarctica, where nearly half of the total ozone column is depleted each September, forming the Antarctic ozone hole. Key evidence includes high levels of ClO, a catalyst for ozone destruction, and the vertical and horizontal structures of ozone depletion, which serve as fingerprints of this process. The unique role of ozone in absorbing solar ultraviolet radiation was recognized in the late 19th century. Ozone depletion has been linked to increased ultraviolet radiation, affecting human, animal, and plant health. Observations of total ozone column abundances since the 1980s show significant decreases, with the Antarctic ozone hole being the most extreme. The ozone hole is caused by heterogeneous chlorine chemistry on polar stratospheric clouds, particularly in cold conditions. This chemistry involves reactions on cloud surfaces that convert chlorine into forms that can destroy ozone. The chemical partitioning of chlorine between active forms that destroy ozone and inert reservoirs is central to understanding ozone depletion. Chlorine forms reservoirs like HCl and ClONO₂, which can be reconverted to active chlorine through gas-phase chemistry. Bromine chemistry also contributes to ozone depletion, especially in combination with chlorine. The long atmospheric residence times of CFCs mean that their effects on ozone depletion will persist for decades. The discovery of the Antarctic ozone hole in the 1980s confirmed the role of chlorine chemistry in ozone depletion. The ozone hole is linked to the presence of polar stratospheric clouds, which facilitate heterogeneous chlorine chemistry. This process is most effective in Antarctica due to colder temperatures and higher frequencies of polar stratospheric clouds. The depletion of ozone in the Antarctic is also influenced by the dynamics of the polar vortex and the transport of air masses. The review highlights the importance of chemical partitioning and the role of chlorine and bromine in ozone depletion. It also discusses the impact of human activities on the atmosphere and the need for reducing emissions to recover the ozone layer. The ozone hole serves as a key fingerprint of chlorine chemistry, with the vertical and horizontal structures of ozone depletion providing evidence of this process. The review emphasizes the need for continued research and monitoring to understand and mitigate the effects of ozone depletion.Stratospheric ozone depletion, driven by human-made chlorofluorocarbons (CFCs), is a major environmental issue of the 20th century. This review outlines the science and history of ozone depletion, focusing on chemical processes and evidence of depletion. Observations show that CFCs have caused about 10% depletion of stratospheric ozone near 40 km, with the most dramatic effects in Antarctica, where nearly half of the total ozone column is depleted each September, forming the Antarctic ozone hole. Key evidence includes high levels of ClO, a catalyst for ozone destruction, and the vertical and horizontal structures of ozone depletion, which serve as fingerprints of this process. The unique role of ozone in absorbing solar ultraviolet radiation was recognized in the late 19th century. Ozone depletion has been linked to increased ultraviolet radiation, affecting human, animal, and plant health. Observations of total ozone column abundances since the 1980s show significant decreases, with the Antarctic ozone hole being the most extreme. The ozone hole is caused by heterogeneous chlorine chemistry on polar stratospheric clouds, particularly in cold conditions. This chemistry involves reactions on cloud surfaces that convert chlorine into forms that can destroy ozone. The chemical partitioning of chlorine between active forms that destroy ozone and inert reservoirs is central to understanding ozone depletion. Chlorine forms reservoirs like HCl and ClONO₂, which can be reconverted to active chlorine through gas-phase chemistry. Bromine chemistry also contributes to ozone depletion, especially in combination with chlorine. The long atmospheric residence times of CFCs mean that their effects on ozone depletion will persist for decades. The discovery of the Antarctic ozone hole in the 1980s confirmed the role of chlorine chemistry in ozone depletion. The ozone hole is linked to the presence of polar stratospheric clouds, which facilitate heterogeneous chlorine chemistry. This process is most effective in Antarctica due to colder temperatures and higher frequencies of polar stratospheric clouds. The depletion of ozone in the Antarctic is also influenced by the dynamics of the polar vortex and the transport of air masses. The review highlights the importance of chemical partitioning and the role of chlorine and bromine in ozone depletion. It also discusses the impact of human activities on the atmosphere and the need for reducing emissions to recover the ozone layer. The ozone hole serves as a key fingerprint of chlorine chemistry, with the vertical and horizontal structures of ozone depletion providing evidence of this process. The review emphasizes the need for continued research and monitoring to understand and mitigate the effects of ozone depletion.