Agriculture is among the world’s largest sources of greenhouse emissions and is the largest source of certain types of anthropogenic nitrogen pollution. But as a source of renewable fuels production and carbon sequestration, agriculture could also be part of the solution to energy security and climate change problems. Similarly, improved management of agricultural nitrogen use could be the key to managing nitrogen pollution in surface- and groundwater systems. If policy makers are to determine how best to develop and implement effective policy interventions to correct environmental problems in agriculture, the critical linkages among demand, supply, land use, nitrogen use, and greenhouse gas emissions must be captured. This paper projects greenhouse gas emissions and nitrogen use from agricultural and forestry practices under baseline and alternative biofuel scenarios in the United States, while accounting for land use competition, production heterogeneity, and a full suite of biofuel production possibilities.