The achievement of satisfactory air quality entails the adoption of one or more air pollution control strategies. Of the four basic strategies available, only air resource management requires the use of air quality models. Atmospheric dispersion models are a subset which can be employed either for fundamental research or for practical decision making. The characteristics of user oriented atmospheric dispersion models are simplicity, clarity, reliability, appropriateness, and practicality. Model performance is determined with reference to accuracy, skill, sensitivity, consistency, generality, integrity, and mechanism. For the suocessful application of air quality models to the decision process, there must be close co-operation between modellers and users.