The document is concerned with the several kinds of flight simulators available today which are valuable tools for research, training, and proficiency measurement. They range from simple trainer type devices useful for learning specific tasks, to very sophisticated ground based facilities and aircraft used for crew training under simulated environmental and operational conditions. The various perceptual phenomena and performance modes observed indicate that it is not physical similarity of devices, but psychological, physiological, and operational realism, which determines realism in simulation. In general, the amount of transfer of training seems closely related to the degree of fidelity which can be provided. (Ten figures and 28 references are included.) (Author/LY)