This book provides an up-to-date synthesis of the understanding of the interaction between the emission of nitrogen, its deposition and impact on the most important components of natural and semi-natural ecosystems. The work consists of contributions from internationally renowned research scientists. Individual chapters deal with the factors and processes related to nitrogen deposition and soils, non-forest vegetation communities, forest ecosystems, and surface waters. The assessment of these impacts is discussed in terms of setting critical loads. The book is aimed at researchers, advanced course students and policy makers/advisors involved with aspects of the impact of air pollution.