The various problems associated with anthropogenic nitrogen enrichment - acidification, climate change, eutrophication, ozone destruction - are common to most countries, and the transboundary nature of the problems requires international dialogue and agreed action to provide solutions. The edited papers in this volume represent the current thoughts of scientists at the leading edge of research into the nitrogen cycle. They were presented at the Third New Phytologist Symposium, held at the University of Lancaster in September 1997.