Simulation may be defined as (1) a technique of modeling (physically, iconically, verbally, or mathematically) some aspects of a real or proposed system, process, or environment or (2) the model (physical, iconic, verbal, or mathematical) of some aspects of a real or proposed system, process, or environment. Simulation may be used to generate information (research); generate new objects, processes, or systems (development); or develop knowledge of skills (instruction). When used for instruction, simulation represents certain elements of real life minus task-irrelevant elements. Given the types of representation of the stimulus situation, the response, and the feedback, classification of "simulations" or "simulators" is possible. Simulation may be used to present information (referential simulation), elicit responses (contextual response simulation), or assess performance (criterion simulation). Four features characterize contextual response simulation: (1) enacted or lifelike responses are made to (2) nonreal stimulus situations that (3) provide feedback to the student vis-a-vis his behavior in the on-going context that (4) offers control. Transfer and motivation are additional factors to be considered. From simulations it is possible to learn winning strategies, principles and relationships, decision-making skills, identifications, procedural sequences, and skilled perceptual-motor acts. (A 104-item bibliography is appended.) (Author/SG)