The present model aims to quantify greenhouse gas (GHG) emissions from changes in agricultural activity on a global scale. It is based on the FAPRI Agricultural Outlook Model, which is used to project changes in agricultural activity in approximately 35 countries and regions covering 13 crops (grains, oilseeds, rice, cotton, sugar) and two major livestock categories (cattle and swine). The FAPRI model is used to project the impact of policy changes on agriculture, and then the GreenAgSiM model is used to calculate the impact of these changes on GHG emissions. The GreenAgSiM model can be used to evaluate the GHG implications of a change in agricultural, bio-energy and environmental policies in the US and elsewhere. It follows closely the guidelines for GHG inventories established by the Intergovernmental Panel on Climate Change (IPCC).