Precision farming involves doing the right things in the right place at the right time. Combine yield mapping systems are documenting considerable yield variation within typical fields and should encourage improved crop management for higher profits and less impact on the environment. Variety choice, pest control, drainage, soil type, soil fertility, tillage practices, crop rotation, plant stands, and topography are a few of the factors causing yield variation. Managing these causes will require a much more detailed, yet holistic approach to crop production. Precision farming tools make on-farm research easier, which should help producers make more informed management decisions.