In 1970 there were slightly less than 200,000 people incarcerated in the United States. By 2007, more than 2.2 million people were incarcerated, and the total number of Americans under criminal justice supervision, including juveniles, people in jail or on parole or probation, exceeded seven-million, or one in a hundred American adults. This dramatic surge in American reliance on incarceration was not inevitable or even predictable. In fact, the origins of mass incarceration were rooted in a period of great doubt about the very utility of prisons that emerged in the mid- twentieth century. How, then, did Americans move toward a total reinvestment in an institution that many experts had declared a failure; and how did they come to accept and indeed embrace the punitive, retributive, hard-line penal philosophy that bolstered mass incarceration?