The approach of precision agriculture (PA) can be viewed as cyclical in nature, involving data collection, development of management plans, implementation of those plans in the field and evaluation of the effort. This chapter examines the characteristics of variable-rate application (VRA) control systems, before going on to consider the implementation of both liquid and dry VRA systems. The chapter reviews a number of detailed VRA case studies and summarizes the current status of research in this field. Finally, the chapter looks ahead to future research trends in the area.