This report documents a method used to define the tillage system used in crop production, based on the percentage of soil surface covered by residue from the previous crop immediately after planting a new crop. Residue estimates were developed for the percentage reduction in residue from a single pass of each tillage implement. The type of tillage used may be a factor in a producer's qualifying for Federal agricultural programs because of conservation provisions in the 1985 Food Security Act and the Food, Agriculture, Conservation, and Trade Act of 1990. The resulting designations are used in conjunction with the Economic Research Service Cropping Practices Survey.