Before there was a podcast, there were the Freakonomics books, by Steven D. Levitt and Stephen J. Dubner. They have won many awards, sold millions of copies around the world, and turned the very word “Freakonomics” into a cultural touchstone. They also inspired Freakonomics Radio and our other podcasts. Someday, Levitt and Dubner may write some more books. For now, these four are there for the reading.