AbstractThis article describes the UBe of simulation to design a flexible computer controlled manufacturing system (FMS).The simulation model described is designed to determi ne the best layout of the operative units of the system and to find a near-optimal control policy to be implemented on the central control processor for real time monitoring of the entire system.The program provides a discrete simulation and is structured in several extremely specialized functionally oriented modules, some of which are user implemented in a man-machine colloquium. The main control modules following suitable optimal criteria such as maximum productivity and minimum cost, have the followv.Tg tasks: to order the activities on the basis of the actual queues, to choose the operative units more profitably in order to carry out these activities by analyzing the actual system status and configuration.To accomplish the simulation purpose, the program supplies the user with numerous statistical parameters giving a significant picture of the behaviour of the single machi nes and of the entire system. This picture will isolate critical items and its analysis may suggest modifications able to improve system efficiency. A practical application of the simulation program to a production center design is also given.