A detailed but accessible overview of the concept of indirect land use change and the way that ILUC emissions are estimated. Identifies factors that determine the size of ILUC effects when biofuel demand increases and shows how they are handled in the most important models used in the U.S. and EU. Over the past decade, the concept of indirect land use change (ILUC) has come from obscurity to become a primary concern for biofuels policy. In the U.S., the Renewable Fuel Standard and California's Low Carbon Fuel Standard now include estimates of carbon emissions from ILUC. In the EU, a European Commission review of ILUC from biofuels resulted in proposed amendments to the Renewable Energy Directive and Fuel Quality Directive that are still being debated by the European Institutions two years later.