This paper describes a digital simulation model of a hypothetical business system and discusses problems pertinent to the construction and use of the model. Constructed in the course of a management control systems research project, the model exemplifies many problems of control and management of a large system, emphasizing information flow, its control, and its use in decision procedures. The model's modular nature permits a variety of experimental uses. The broad scope of the modeled system posed implementation problems which were resolved by the development of a general simulation capability, called SIMPAC, whose main features are described. "Management Technology", ISSN 0542-4917, was published as a separate journal from 1960 to 1964. In 1965 it was merged into Management Science.