This chapter provides a review of decision support systems (DSS) in agriculture and addresses several key questions about them. Why are they important, and why are they necessary for the future? What kind of systems currently exist? Different aspects of agricultural DSS design, implementation and operation are covered. These aspects include the fundamentally spatial consideration of DSSs, the need for and use of sensor technology within such systems, modelling and software components, system-operator interfaces, the potential (and current) use of DSSs for directly controlling agricultural management, and a discussion of what is needed to make DSSs more successful and widely-used in agriculture.