Defending society against natural hazards is a high-stakes game of chance against nature. Recent hurricanes, earthquakes, and tsunamis show that society often does poorly. Sometimes nature surprises us, when an earthquake, hurricane, or flood is bigger or has greater effects than expected from detailed natural hazard assessments. In other cases, nature outsmarts us, doing great damage despite expensive mitigation measures or causing us to divert limited resources to mitigate hazards that are overestimated. Much of the problem comes from the fact that formulating effective natural hazard policy involves using a complicated combination of science and economics to analyze a problem and explore the costs and benefits of different options, in situations where the future is very uncertain. Because mitigation policies are typically chosen without this kind of analysis, the results are often disappointing. This book explores how we can do better.