Author Stephen Dubner met economist Steven Levitt when The New York Times Magazine asked Dubner to profile the young professor. Each believed the other’s profession was filled with incompetent people, but they admired each other. Dubner found that Levitt approached economics less as an academic than as an explorer who studies “the riddles of everyday life […] He sifts through a pile of data to find a story that no one else has found” (xxiv-xxv).

When the interview came out, Levitt was showered with requests for help, from a bagel salesman to the CIA, all of whom wanted him to apply his genius to the questions that troubled them. Publishers asked Levitt to write a book. He agreed, but only if his co-author was Dubner.

The Introduction surveys the ideas explored throughout the book, beginning with crime in the 1990s. During the early 1990s, increasing crime rates brought anxiety to Americans, who feared a “superpredator” criminal type, “a scrawny, big-city teenager with a cheap gun in his hand and nothing in his heart but ruthlessness” (1-2). Experts predicted a new crime wave. Instead, by 2000, all types of crime had dropped to rates not seen since 1965.