Nutrient use efficiency can be defined many ways, but the definition used most commonly by farmers and crop advisers is the crop output per unit of nutrient input. Nutrient deficits occur throughout the United States, and as crop yields and nutrient removal increase, there is a greater need to be efficient with nutrient inputs. In contrast, nutrient surpluses in some watersheds are associated with growing environmental concerns. Most of these environmental concerns involve nitrogen and phosphorus discharges from farm fields and potential linkages to increased algal growth and decreased oxygen concentrations in surface waters. One of the most recognized watersheds in the United States is the Gulf of Mexico watershed, which accounts for the majority of the principal crop acreage and nutrient use in the United States. Goals have been established for improvements in the waters within the Mississippi Basin and a reduction in the size of the hypoxic area in the Gulf. To achieve these water quality goals, nutrient management changes will have to occur and the economics of the changes will have to be closely evaluated. As policies are developed to mitigate nutrient related water quality problems, and as farmers strive to maintain global competitiveness, estimates of nutrient use efficiency may become increasingly important. We are all interested in improving the efficiency with which we simultaneously accomplish all system level objectives: productivity, profitability, sustainability, and environmental protection.