Although agriculture uses large amounts of energy for growing and processing foods, it also generates even larger amounts of unused energy in the form of crop residues. For the successful utilization of this energy source at the farm or food-processing level, a simple, low-cost method of converting residue energy to heat or shaft horsepower is needed. Such a method is gasification. The theory of gasification is reviewed and its historical application to crop residue is presented. Several potential applications are discussed.