This chapter examines the use of wave energy device (and array) models for model-based control. To date, a wide variety of control strategies for wave energy converters (WECs) have been proposed, each with some requirement for a mathematical description of the wave energy device. Three example WEC control strategies, from relatively simple to one based on numerical optimization, are presented, in order to understand the mathematical modelling requirements for WEC control systems. In addition, the close link between control design and WEC optimization is explored. The optimal device geometry, as well as optimal WEC array layouts can be strongly influenced by the control system adopted for the device/array and the chapter articulates this two-way interaction. Finally, since many WEC control strategies are noncausal, the issue of short-term wave forecasting is addresse