Biodiesel, produced from seed oils or animal fats via the transesterification process, has been the focus of biofuel production because of its potential environmental benefits and because it is made from renewable biomass resources. Biodiesel can be blended with conventional diesel fuel in any proportion and used in diesel engines without significant engine modifications. In recent years, the sales volume for biodiesel in the U.S. has increased dramatically from about 2 million gallons in 2000, to 75 million gallons in 2005, to 250 million gallons in 2006. This book explores the effects of biodiesel on diesel engine nitrogen oxide and other regulated emissions.