Changes in risk perception have been used in various contexts to explain shorter-term developments in financial markets, as part of a mechanism that amplifies fluctuations in financial markets, as well as in accounts of "irrational exuberance." This approach holds that changes in risk perception affect actions undertaken in risky situations, and create a discrepancy between the risk attitude implied by those actions and the a priori description of risk attitude as summarized by the Arrow-Pratt coefficients of risk aversion. The author characterizes this discrepancy by introducing the notion of risk perception within the expected utility theory, and proposes the concept of implied risk aversion as a summary measure of risk attitudes implied by agents' actions. Properties of implied risk aversion are related to an individual's future outlook. Key ideas are illustrated using an asset-pricing model.