There is an increasing focus on the concept of integrated systems control in applications to industrial systems, e.g. chemical processing and steel. Motivating factors include (i) rising costs (and limited availability) of energy and various raw materials, (ii) competitive pressures to improve production efficiency, labour productivity, flexibility, etc., and (iii) more stringent government regulations concerning environmental impact and product quality. At the same time, the tools for effecting systems control (analytical techniques, systems methodology, computer hardware and software) have become increasingly powerful, reliable, and available. Here, control is considered in a very general context to include all aspects of decision-making applied to the operating system, ranging from process control to production scheduling and planning. The digital computer plays a very central role in making feasible the modern industrial control system where it serves the functions of information processing, on-line control, and decision-making in real time through man-machine interaction. The hierarchical control approach provides a conceptual framework for organizing and implementing integrated control of large industrial systems. Various aspects of the control hierarchy are considered; these will be described in the context of integrated systems control applied to the steel industry.