The depletion of stratospheric ozone due to anthropogenic emissions of long-lived substances containing chlorine and other halogens was first identified as a matter of international concern in the mid-1970s and has received increasing attention since the mid-1980s after the discovery of the ozone hole. Today, in spite of the successful application of the Montreal Protocol and its amendments, the atmospheric halogen loading is still above natural levels and will remain so until the middle of this century. Monitoring of stratospheric ozone therefore remains extremely important, as the ozone layer has yet to recover from the atmospheric halogen loading caused by human action. Moreover, climate change also has an influence on stratospheric ozone while evidences that changing tropospheric ozone levels impact climate are becoming increasingly clear.