Following a short historical introduction the problems encountered in the control of different types of industrial processes are compared. Processes are divided into batch processes, continuous processes operating in steady state for long periods and quasi-batch processes, in which the control, when going from one steady state to another, is important. The modelling and development of control strategies for a narrow, hot-steel-strip rolling mill are discussed in detail by way of illustration and it is demonstrated how an iterative procedure can be used with ‘ feedforward ’ to give a near optimal control, advantage being taken of the inevitable time-delays that occur between stands. In the Appendix the formal mathematical relationships underlying the modelling and control of different manufacturing systems are set out and discussed while in § 4 the ways in which these techniques can at present be used are described. Finally, the developments which may be expected during the next few years are discussed.