This paper presents a modification to the functional simulation technique which allows the user to perform simulations of systems at increasing levels of detail by making only minimal changes in the description of the system. Functional simulation is easy to imple ment because the functional simulation model defines all the system control parameters necessary for simu lation. The investigator designing the simulation need not be concerned with implied parameters. To extend the technique of functional simulation to multilevel functional simulation (MLFS) requires only a small amount of additional program, but it provides a significant increase in capability.