The effects of air pollution on biota may be subtle and elusive because of their interactions with natural stresses. Studies based on a network of sites in the Carpathian Mountains form the core of the content presented during this workshop. To this core are added key components on ecological sustainability, overviews on forest health in Europe and the world and several in-depth case studies. This book provides a state-of-science report on the effects of air pollution (with a special emphasis on ozone) on the composition, structure and functioning of forests, particularly in the Carpathian Mountains.