This special section deals with the simulation of complex systems, such as computer, communications, and manufacturing systems—specifically focusing on stochastic discrete event simulation. Such systems are typically 1990 modeled by a network of queues, in which jobs compete for the system's resources. For example, in an on-line computer database system, the jobs would represent transactions, and the system's resources would include processors, disks, main memory, data locks, etc. Since job arrival patterns and resource requirements are unpredictable, such systems are inherently stochastic (random). As these systems increase in complexity, it becomes increasingly difficult to build analytically tractable performance models; thus simulation, because of its versatility, often becomes the only viable analysis technique. This issue contains articles which span a broad range of current topics in simulation, including. © 1990, ACM. All rights reserved.