In today's complex industrial processes, automated control systems are a necessity. However, is complete automation the answer? Whereas control system automation provides predictable, consistent performance, it is lacking in human judgment, adaptability, and logic. Although humans provide these, we are unpredictable, inconsistent, and subject to emotions and motivation. To maximize system performance, should we automate humans out of the system? ... or ... Do we maximize human input and lose efficient, consistent, error free system performance? The answer is likely somewhere in the middle of these two extremes and different for each system and situation. This paper provides a review of the existing literature covering control schemes and parameters that determine system performance. It attempts to help answer the questions "How can we minimize human error while still maximizing system performance?" and "What is the right human-machine mix?" (C) 2005 American Institute of Chemical Engineers.