Excess reactive nitrogen (Nr) compounds in the environment are associated with many large-scale environmental concerns, including eutrophication of surface waters, toxic algae blooms, hypoxia, acid rain, nitrogen saturation in forests, and global warming. In addition, reactive nitrogen is associated with harmful human health effects caused by air pollution and drinking water contamination. Reactive nitrogen includes all biologically active, chemically reactive, and radiative active nitrogen compounds in the atmosphere and biosphere of the earth, in contrast to non-reactive gaseous N2. The EPA and other federal and state agencies have implemented programs to reduce the risks posed by excessive nitrogen, but a more comprehensive and integrated approach is needed to manage the use of nitrogen in a way to achieve its benefits, such as fertiliser for food production, and mitigate its damages as it is introduced to and cycles repeatedly through the environment in different forms and media. This book examines the flows, effects and management options of reactive nitrogen in the environment.