The very mention of nuclear terrorism is enough to rouse strong reactions, and understandably so, because it combines the most terrifying weapons and the most threatening of people in a single phrase. The possibility that terrorists could obtain and use nuclear weapons deserves careful analysis, but discussion has all too often been contaminated with exaggeration, even hysteria. For example, it has been claimed that nuclear terrorism poses an existential threat to the United States.

This Adelphi Paper develops a more measured analysis of the risk of terrorists detonating a...