This volume provides a unique collection of contributions addressing both the too much and too little sides of the nitrogen story. Building on analyses started at the 6th International Nitrogen Conference, Kampala, the book explores the idea of just enough nitrogen: sufficient for sustainable food production, but not so much as to lead to unsustainable pollution and climate problems. The range of nitrogen threats examined, solutions evaluated and science-policy analyses presented here has provided the foundation to agree the Kampala Statement-for-Action on Nitrogen in Africa and Globally, as reported in this volume. Humanity today faces unprecedented challenges: How to feed a growing population? How to reduce air pollution, water pollution and climate change? How to handle regional differences in an era of increasing globalization? These questions are at the heart of this edited volume which examines the multi-dimensional nature of the global nitrogen challenge.While humans have massively altered the nitrogen cycle, the consequences have become polarized. Some regions have too much nitrogen, associated with pollution and wasteful use of a valuable resource, while other regions have too little nitrogen, leading to constraints on food production and depletion of soil nutrient stocks. The volume provides a unique collection of contributions addressing both the too much and too little sides of the nitrogen story. Building on analyses started at the 6th International Nitrogen Conference, Kampala, the book explores the idea of just enough nitrogen: sufficient for sustainable food production, but not so much as to lead to unsustainable pollution and climate problems. The range of nitrogen threats examined, solutions evaluated and science-policy analyses presented here has provided the foundation to agree the Kampala Statement-for-Action on Nitrogen in Africa and Globally, as reported in this volume. Together, the contributions in this book are now informing actions by the International Nitrogen Initiative (INI) in working with the United Nations Environment Programme and others to establish the International Nitrogen Management System (INMS). A key outcome has been to catalyse development of the first Resolution on Sustainable Nitrogen Management, as adopted by the fourth UN Environment Assembly (UNEA/EA.4/Res.14). The work is written for researchers and policy makers and all those interested in seeing how sustainable nitrogen management can contribute to meeting many of the UN Sustainable Development Goals.