This paper describes how the substantial increased use of ethanol in gasoline in the United States, spurred by a steady rise in the price of gasoline from 2006 to 2008, led to a reduction in greenhouse gas emissions but an increase in food prices in the country. The economic viability of producing corn ethanol and its relationship to the climate and food prices is assessed in detail. And, the authors explain ethanol production and consumption under import tariffs, federal mandates and the production subsidy.