Process control is an essential part of the desalination industry that requires for operation at the optimum operating conditions an increase in the lifetime of the plant and reduction of the unit product cost. A review is presented for the commonly used and newly developed control and instrumentation in MSF and RO plants. Process control may be as simple as an on/off valve that is triggered upon offset of the system measured parameters from the desired set-point. More classical and commonly used controllers have combined proportional, integral, and derivative (PID) systems. Also, proportional/integral (PI) controls are used in industry. Controls selection aims at fast response, high stability, and minimum disturbance to the system. Less common controllers include fuzzy logic-based systems. Early testing of such systems shows the need for mathematical analysis of various control loops within the plant, development of control rules, and development and testing on industrial scale. Supervisory systems such as model predictive control are also considered to obtain an integrated control systems of the whole plant. It should be stressed that although the desalination plants are highly complex, accurate and detailed mathematical models for steady state and process of various desalination processes are found in the literature. Such models are necessary for studying plant performance, various control strategies, and forms an essential part for any serious analysis and development of novel and new control systems.