Of course, we could imagine using a single optimizing controller who stabilizes the processwhile at the same time perfectly coordinates all the manipulated inputs based on dynamic on-line optimization. There are fundamental reasons why such a solution is not the best, even with today’s and tomorrows computing power. One fundamental reason is the cost ofmodeling, and the fact that feedback control, without much need for models, is very effective when performed locally. In fact, by cascading feedback loops, it is possible to control largeplants with thousands of variables without the actual need to develop any models. However, the traditional single-loop control systems can sometimes be rather complicated, especially if the cascades are heavily nested or if the presence of constraints during operation make it necessary to use logic switches. Thus, model based control should