Abstract: When sufficient computing power is available, dynamic simulation can be used as a source of motion for real-time, interactive virtual environments. In this paper, we explore techniques for reducing the computational cost of simulating groups of creatures by using less accurate simulations for individuals when they are less important to the viewer or to the action in the virtual world. The less accurate, or lower level of detail, simulations can be dynamic with fewer degrees of freedom, hybrid kinematic/dynamic, or purely kinematic. As a test of the effectiveness of this approach, we implemented an environment with dynamically simulated legged creatures. Because the creatures switch smoothly among different levels of detail for the underlying simulation, we can achieve real-time performance for a larger group of creatures than would be possible if each creature were dynamically simulated. To be useful in this test case, the method must meet two criteria: the outcome of the game must be essentially unchanged and the viewer's perception of the motion must be the same. While it is not possible to make definitive measurements of these criteria, we assess the performance gain from using different levels of detail and make a preliminary assessment of the effect that the decreased accuracy has on the outcome of the sample game.