The principles of optimizing process control are elucidated by weighing the merits of hill-climbing, feedback, methods against model, feedforward, methods. It is shown that the advantages of the two methods can be employed at both the optimizing and the stabilizing control levels of a chemical plant. A simple static model containing appropriately chosen non-linearities is being used in a feedforward control loop and updated regularly by feedback in an openloop computer control system, results of which are given. Finally, it is shown that such a model can also be used for statistical evaluation of computer control methods.