In this entry, the role of prediction models for medical decision making is discussed. Decision rules can be based on prediction models and are important for more individualized decision making. Prediction models have potential applications in both medical practice and research. Prediction models are ideally derived from large-volume, high-quality empirical data to quantify the relationship between a set of predictors and a diagnostic or prognostic outcome. Model development needs to be followed by model validation and an analysis of the model's impact on decision making and outcomes of individual subjects.