Ethanol is currently the only liquid alternative fuel officially endorsed and subsidized by the governments of many western countries. It is produced by fermentation of starch crops such as corn in the USA or sugar cane in Brazil. Its properties and fuel characteristics are the closest to those of gasoline, and modification of existing vehicles to use ethanol or ethanol blends is straightforward and inexpensive. Currently, all gasoline in the USA and in most European countries contains ethanol in ratios from 5% to 15%, serving as an octane enhancer. In all countries in which it used as an alternative fuel or gasoline additive, it is heavily subsidized. In the USA, this takes the form of E85, an 85% (nominal) volumetric blend with 15% gasoline. It has always been the subject of disagreement and political debate citing countless conflicting studies concluding that it may or may not be environmentally beneficial or sufficiently energy positive to justify its designation as a renewable transportation fuel. This chapter discusses most aspects of ethanol as a motor fuel, from its production from grain crops through the modifications required for its substitution for gasoline for automobiles.