In this chapter, we will address the questions raised in the introduction by considering both scientific and societal issues. As we investigate the properties of ozone, we soon find that some knowledge of its molecular structure and the nature of light are needed to understand how ozone acts in the stratosphere to filter the Sun's harmful radiation. A consideration of some fundamental properties of atomic structure is also necessary. These ideas are then used to predict the molecular structures of a number of substances, including ozone. A discussion of sunlight in particular and radiation in general follows. You will find that light is strangely schizophrenic — it can behave both like waves and like little particles of energy. The particulate properties are especially useful in describing how ozone and oxygen molecules absorb ultraviolet radiation and how radiation damages biological materials. The formation and fate of ozone and its distribution in the atmosphere are considered. We then turn to an analysis of the various mechanisms for the depletion of stratospheric ozone, some involving naturally occurring chemicals and others involving synthetic compounds. Among the latter are the chlorofluorocarbons, whose properties and uses are discussed at length. The following section describes the stratospheric interaction of chlorofluorocarbons and ozone. After a discussion of the Antarctic ozone hole, the chapter concludes with a consideration of the social and technical problems associated with reducing chlorofluorocarbon emissions and developing substitutes.