This article summarizes the findings from three laboratory studies investigating the content of decision makers' mental models and the relationship between mental models and performance on microworld simulations. 1 We examine three different components of mental models: perceived causal relationships, high-level strategies, and decision rules. The findings advance our understanding of the effects of different levels of complexity, different causal diagram presentations, and different learning paths on mental models and performance.The psychological core of understanding … consists of having a "working model" of the phenomenon in your mind. If you understand inflation, a mathematical proof, the way a computer works or DNA … you have a mental representation that serves as a model. (Johnson-Laird, 1983, p. 3) Each of us uses models constantly. Every person in private life and in business instinctively uses models for decision making. The mental images in one's head about one's surroundings are models. … A mental image is a model. All decisions are taken on the basis of models. (Forrester, 1971, p. 55)