Catastrophic risks are much greater than is commonly appreciated. Collision with an asteroid, runaway global warming, voraciously replicating nanomachines, a pandemic of gene-spliced smallpox launched by bioterrorists, and a world-ending accident in a high-energy particle accelerator, are among the possible extinction events that are sufficiently likely to warrant careful study. How should we respond to events that, for a variety of psychological and cultural reasons, we find it hard to wrap our minds around? Posner argues that realism about science and scientists, innovative applications of cost-benefit analysis, a scientifically literate legal profession, unprecedented international cooperation, and a pragmatic attitude toward civil liberties are among the keys to coping effectively with the catastrophic risks.