Emissions of ammonia, the airborne transport of ammonia and its fate were the focus of discussion at the third 'Shared Resources' Airsheds and Watersheds workshop, held November 15-16, 2000 in Dewey Beach, Delaware. Two previous workshops addressed the regional impacts of atmospheric nitrogen deposition, but largely from the standpoint of nitrogen oxide (NO-x) emissions-less attention was given to ammonia emissions. Scientific studies now indicate that ammonia emissions may result in a significant and growing form of nitrogen input to terrestrial and aquatic ecosystems. Airborne nitrogen compounds in wet and dry deposition, along with nitrogen from fertilizers, sewage, and industrial discharges, are a source of nutrients to receiving waters via surface water runoff, ground water flow and direct inputs. Current estimates are that atmospheric nitrogen deposition can contribute from 10 to over 40% of the 'new' nitrogen enrichment of coastal and estuarine waters. Since ammonia is often a preferred form of nitrogen for biological activity, its increasing availability could cause fundamental changes in aquatic algae communities. Additionally, air quality experts recognize that ammonia plays an important role in the formation of fine particulate matter, which can affect human health and degrade visibility. The need for managing ammonia emissions is demonstrated in the Netherlands where the environmental impacts are clearly visible.