In this paper we propose a new approach to parallel and distributed simulation of discrete event systems. Most parallel and distributed discrete event simulation algorithms are concerned with the simulation of one “large” discrete event system. In this case the computational intensity is due to the size and complexity of the simulated system. In contrast, we are interested in simulating a “large” number of “medium sized” systems. These are variants of a “nominal system” with different system parameter values or operation policies. The computational intensity in our case is due to the “large” number of simulated variants. Many simulation projects such as factor screening, performance modeling, and optimization require system performance evaluations at many parameter values; and others, we believe, could significantly benefit from them. There is considerable work in the literature on stochastic coupling of trajectories of parametric families of stochastic processes. Our approach can be viewed as the simulation of the coupled trajectories. We use a single clock mechanism that drives all trajectories simultaneously, hence the approach is called Single Clock Multiple System (SCMS) simulation. The single clock synchronizes all trajectories such that the “same” event occurs at the “same” time at all systems. This synchronization is the basis of our parallel and distributed algorithms. We focus on a particular implementation of the SCMS simulation using the so-called Standard Clock (SC) technique and also on the massively parallel implementation of the SC algorithms on the SIMD Connection Machine. Orders of magnitude of speedup is possible. Furthermore, the possibility of concurrent performance evaluation and comparison at many system parameter values offers new and significant opportunities for performance optimization.