The subject of this dissertation is knowledge representation for expert systems applied to chemical process control. For the purposes of the dissertation, control system design is defined as establishment of the necessary single input - single output controllers for regulatory and constrained control. One of the most difflcult tasks in creating an expert system to solve any problem is organization of the knowledge such that creation, modification, and extension of the expert system can progress smoothly. An introduction to expert systems and the way knowledge is represented within them is given. Included in the introduction is a description of the requirements of an expert system shell to be used to solve the control design problem. Idiomatic control and the goal tree success tree model for knowledge are presented as organizational tools to represent the problem solution prior to expert system construction.