Risk analysis and risk assessment have been with us long enough for the terms to sound familiar to most people. Standard fare for the nuclear power industry and the military for a half a century or more, risk assessment is now a routine aspect of environmental management, public health and individual medical decision making. There have been popular books on risk, and the current poker craze will likely spread risk concepts to an even wider (and younger) audience. Yet, despite all of this extensive and varied experience, we the analysts and practitioners have not done nearly enough to explain to the people who need to know what they need to know – especially the uncertainty inherent in risk estimates. There are many instances in which the failure to communicate risk information accurately or completely has had an important and material impact on decisions and actions. I have been involved in some of these, ranging from local plans for water management to national decisions about nuclear waste. I have seen first hand the effects of poorly done risk asse- ments and bad risk communication, and especially the way in which the uncertainly of risk estimates is handled (or mishandled). The con- quences of doing this wrong are high. It’s high time that we addressed this gap in understanding, and this book is an excellent and important step in doing so.