Simulations, which can be defined as formalized techniques for studying complex systems by manipulating the variables in a scaled-down model and observing the results, are useful instructional tools. They provide individualized, self-paced, learner-controlled education, offer discovery experiences which are realistic, and promote problem-solving, decision-making, and immediate feedback. They seem to motivate students and provide them with a means of studying complex systems. Limitations of simulation include the tendencies to over-simplify and over-systematize reality and to stereotype complex situations. Simulations will be even more useful if they are systematically developed, with instructional design following these steps: 1) analysis of instructional content, 2) specification of objectives, 3) definition of target audience, 4) identification of suitable simulation topics, 5) analysis of the feasibility of each topic, 6) design of the simulation, and 7) evaluation. This kind of systems approach to design will remove educational simulations from the realm of the haphazard and provide educators with a demonstrably effective instructional tool. (PB)