Anthropogenic alterations in the nitrogen cycle, dominantly through synthetic fertilizer applications, have allowed for greater crop production since the nineteenth century. However, these changes have also allowed for rapid increases in environmental adverse nitrogen loss pathways such as nitrate leaching, and nitrous oxide emissions. Advancing knowledge on how nitrogen cycling processes are impacted by environmental conditions and management practices provides an insight in how the NUE of cropping systems can be increased. In order to improve the NUE of cropping systems, nitrogen supply must be re-synchronized with crop demand; therefore, supporting productivity whist reducing economic and environmental losses. To accomplish this, a detailed understanding of nitrogen fixation, mineralization, volatilization, nitrification and denitrification is required. This chapter outlines the recent advances in knowledge surrounding nitrogen cycling processes, and the main issues researchers and farmers are presented with when attempting to optimize productivity whilst minimizing adverse economic and environmental nitrogen losses.