The use of corn based ethanol as a supplement or replacement of motor fuel gasoline has many champions as well as detractors.  In this presentation I attempt to separate hype from facts and wishful thinking from realistic forecasts.  The production of corn based ethanol has physical limits based on land required to grow its primary input.  It also has economic limits based on the cost of inputs relative to the cost of the fuel it replaces and the value of the environmental and other benefits its use may provide.  By exploring these limits and the likely consequences of increased production on other prices, I hope to inform a better understanding of the role of corn based ethanol in the economy.