Business, academia, industry, and the military require well trained personnel to function in highly complex working environments. To reduce high training costs and to improve the effectiveness of training, training system developers often use sophisticated training media such as, simulators, videodisks, and computer-based instruction. The designers of these training media are continually striving to provide maximum training effectiveness at minimum cost. Although literature is available on the implementation and use of specific training media, there is little guidance on a major feature that is central to these media. All of these media present the learner with an interactive simulation of the real world. Effective training system design can be facilitated if the requirements of the real-world task are properly included in training. A conceptual bridge is necessary to link these actual task requirements to the characteristics of the training system. This book provides such a conceptual bridge. The need for improved training is critical in the area of equipment operation, maintenance, and decision making tasks. For example, the importance of improved operator training in the nuclear power industry has become paramount since the Three Mile Island accident and the more serious accident at the Chernobyl reactor in the U. S. S. R. Technology, such as the availability and power of computers, offers a wider variety of training options, but requires additional training system design decisions