The topic of this book is the interdependence of stratospheric ozone depletion and climate change. The purpose of this introductory chapter is to lay the foundations, which are necessary for the understanding of the specialized chapters constituting the central portion of this book. In this chapter the basics of stratospheric chemistry are described; ozone production and ozone loss through catalytic cycles and the distribution of ozone in the stratosphere resulting from the interaction of stratospheric ozone chemistry with the stratospheric circulation (the so called Brewer-Dobson circulation). The anthropogenic release of chlorofluorocarbons and other ozone-depleting substances has led to a strong perturbation of the ozone layer. The temporal development of the major ozone-depleting substances in the atmosphere is discussed, focusing both on the rapid increase in ozone-depleting substances in the atmosphere since 1960 and the decline observed today and projected to continue due to the success of the Montreal Protocol and its adjustments and amendments in reducing global production and consumption of these substances. One consequence of the accumulation of ozone-depleting substances in the atmosphere is the ozone depletion observed today in the upper stratosphere peaking at 40km with a decline between 1980 and 1996 of about 10%. The most severe ozone depletion, however, is observed in the Antarctic “ozone hole”, where mean column ozone has been about 40% below 1980 values for the past 15 years. Severe ozone depletion is also observed in recent cold Arctic winters, with the hitherto strongest loss having occurred in winter 2010–2011. Polar ozone depletion occurs because a set of chemical and meteorological processes interact in a way leading eventually to precipitous chemical loss of ozone in springtime. In response to reductions in ozone depleting substances in future decades, stratospheric ozone is projected to recover. However, ozone recovers differently in different regions and at different altitudes in the stratosphere. Further, ozone will not simply recover to 1980 or 1960 values, rather the development of stratospheric ozone over the coming decades will be determined by both substantial reductions in ozone-depleting substances and changes in the stratosphere caused by climate change. Finally, model studies indicate that, had no controls on ozone depleting substances been put into effect, by the middle of this century a severe global depletion of ozone (reductions by more than a factor of two globally) would have developed.