The variability of crops, soils, and pests within crop production fields has led to attempts to understand those variations and to manage crop production accordingly. The rapidly expanding research and development on the management and control of crop production according to in-field variations is reviewed. The various stages and components of this spatially-variable control are classified and presented along with a proposed terminology and notation. Advances in component technologies (sensors, actuators, locators, geostatistics, geographic information systems) and their integration should reduce crop production costs and be environmentally advantageous.