What's Prison For? examines the "incarceration" part of "mass incarceration." What happens inside prisons and jails, where nearly two million Americans are held? Bill Keller, one of America's most accomplished journalists, has spent years immersed in the subject. He argues that the most important role of prisons is preparing incarcerated people to be good neighbors and good citizens when they return to society, as the overwhelming majority will.

Keller takes us inside the walls of our prisons, where we meet men and women who have found purpose while in state custody; American corrections officials who have set out to learn from Europe's state-of-the-art prison campuses; a rehab unit within a Pennsylvania prison, dubbed Little Scandinavia, where lifers serve as mentors; a college behind bars in San Quentin; a women's prison that helps imprisoned mothers bond with their children; and Keller's own classroom at Sing Sing.

Surprising in its optimism, What's Prison For? is an indispensable guide on how to improve our prison system, and a powerful argument that the status quo is a shameful waste of human potential.