Three aspects of the use of marketing models should be highlighted. First, marketing models are an aid to the decision maker, not a replacement. Marketing models often can help the manager make a better decision, but models do not make executive decisions by themselves. Second, marketing models have come to a point in their evolution where they should be viewed by managers as useful tools, not as academic curiosities. In particular, a model-building approach known as decision calculus seems well suited to operational needs of managers, especially those who have not yet used models. Third, model building in marketing covers a broad range of activities and models can be useful to managers in many different ways. Two cautionary points must be made. First, successful models need to be custom fitted to organizations and management problems. This collection should be used only as a foundation and must be coupled with considerable work to apply a model-building approach. Second is a reminder that models are difficult to implement.