This publication originates from the NATO Advanced Study Institute on Environmental Radiation: Impact on Ecosystems and Human Health and Predictive Models, held in Pisa, Italy, in June 2001. The book offers not only basic information on the action mechanisms of UV radiation on ecosystems and various biological systems, but also a picture of the possible scenarios of the long-term global increase of environmental UV radiation, with emphasis on the research aspects aimed at the proper quantitative assessment of risk factors and the formulation of reliable predictive models. The purpose of the authors is to present a critical discussion on how changes in UV radiation will affect ecosystems and the biological processes needed to sustain life on Earth and to provide useful hints for future actions of governmental and international agencies, as well as non-governmental organizations. The book is structured in four sections: the first one is devoted to a general overview of the consequences of ozone depletion and to the basic concepts of radiation measurements and monitoring; the other three sections are devoted to the effects on plants, aquatic ecosystems and human health.