Risk management has received increasing attention in recent years, both from academics and from practitioners. The heightened interest is the result of a number of coincident secular trends, including increased investment in volatile emerging markets and the growing role of capital markets in both developed and emerging economies, as well as the introduction of volatile financial innovations. Risk management has also attracted attention as a result of the repeated and well-publicized failures associated with its implementation. Despite the increased attention paid to risk management, frequent instances still occur when sophisticated investors or firms experience sudden, unexpected, and devastating losses. This article discusses failures in risk management, why they occur, and what can be done to reduce their occurrence. The author discusses the nature of risk and the objectives of risk management. He argues that intuitively attractive conceptual simplifications often create significant errors in risk measurement. He describes such failures in risk management and goes on to discuss the implications, both for managers and for regulators.