This paper discusses the development of technology designed to simulate hypothetical personality structures and to predict specific behaviours as a consequence of personality and situational interactions.4 This device should be useful in theoretical psychology to pose questions of the "What would happen if...?" variety. The program can also evaluate a different kind of questions, "Given the present personality structure of an individual, as a set of dependent variates, what might one predict his behaviour to be if...?" Examples are given of the use to which the personality simulator has been put. Some potential uses are suggested.