This paper is presented in honor of Dr. Arvin R. Mosier and his contributions to advance our understanding of nitrogen (N) and nitrogen management in the Great Plains cropping systems. A review of three decades of his research in N will be covered. During this period, Dr. Mosier made significant advances in the understanding of N dynamics in soils and the use of N management practices to reduce its losses. Nitrogen (N) is an essential nutrient needed for maintaining high yields in cropping systems. If we are to maximize NUE while maintaining or increasing yields, we need to understand N in the system, its pathways and how to reduce its losses. The N cycle is an important source of nitrous oxide (N2O), a trace gas that contributes to potential global warming. Dr. Mosier contributed to fundamental advances in our understanding of how N management practices, such as nitrification inhibitors, timing of application of N, source of N, controlled release fertilizers and others, can be used to reduce N losses. Dr. Mosier's research was key in assessing how N dynamics in the Great Plains cropping systems impact N2O emissions and potential for implementation of mitigation management practices to reduce N2O losses. Dr. Mosier's research covering the application of mass spectrometry methods for N management and NUE studies in Great Plains will also be covered.