A broad view of the traditional operations model, suggesting that any device be accepted as a model if it provides a logical means of predicting and comparing the outcomes of alternative actions, regardless of its representative features or its efficiency in optimization. Illustrative of this extended type of model is Delphi, an iterative procedure for eliciting and refining the opinions of a group of people by means of a series of questionnaires. While much remains to be learned about Delphi and the use of expertise, its potential is considerably wider than published applications indicate. Industrial and urban planners, research managers, and policymakers have shown extensive interest. Suggested applications range from the drafting of diplomatic notes and long-range political forecasting to determining what products to market. Because it can be used to allocate resources rationally and to force explicit thinking about the measurement of benefits, Delphi offers a hope of introducing cost-effectiveness thinking to a wide range of problems where conventional models are difficult to formulate.