Operations research is defined as the application of scientific or quantitative methods to problems involving the operations of a system, which are directed toward obtaining optimal solutions. The goal, as applied to mental health systems, is the establishment of a "best" improvement path which can be implemented with minimum uncertainty. The uncertainty can be minimized by utilizing a model, a representation, of the system which can be manipulated, torn apart, reconstructed, all without risk to the real system. The concepts involved in this "model" approach are viewed as the basis for solving a wide range of problems encountered in designing a community mental health system. Three examples are given: (1) the development of an expansion path for community services, which concerns the effective distribution of resources; (2) a network analysis which focuses on how many separate cycles a client goes through at an agency, their duration and resultantly, the incumbent demand for a comprehensive information system; and (3) an agency clustering/problem clustering model which focuses on clients' problem and condition sequences, and the implications for more efficient and orderly service delivery. (TL)