Site-specific nutrient management systems were created to manage for spatial and temporal variability in biophysical factors that determine the availability and demand of crop nutrients. These systems differ among geographical regions in the information utilized and the way they operate to accomplish their common purpose: namely, improve nutrient use efficiency and balance trade-offs between profitability and environmental concerns. This chapter looks at system inputs that are used to inform site-specific nutrient management, illustrates system processes and outputs with examples from the Midwestern and Western U.S., and identifies trends and further developmental needs.