This synthesis is the final report from the International SCOPE Project on Nitrogen Transport and Transformations: A Regional and Global Analysis. SCOPE (the Scientific Committee on Problems of the Environment) authorized the Nitrogen Project because of the need to better understand how humans have altered nitrogen cycling globally and at the scale of large regions. The project has synthesized information through a series of workshops over the past 8 years, involving over 250 scientists from over 20 different nations. Papers in this volume explore the extent to which human activity has affected the nitrogen cycle in terrestrial regions and in the world’s oceans, and discuss the implications of accelerated nitrogen cycling for nature and society.