The booklet summarises current understanding of how changes in the ozone layer affect human health, not only in the world we live in but also in the ‘World Avoided’. That is the world we would have lived in had we failed to control ozone depleting substances. By examining the ‘World Avoided’ we clearly see, to echo the words of the Vienna Convention, the magnitude of the “harmful impact on human health and the environment” that we have prevented through the effective implementation of the Montreal Protocol.