The contours of mass incarceration are, by now, broadly familiar. The U.S. incarceration rate began an unprecedented ascent in the 1970s. This trend continued through 2007, when 760 of every 100,000 U.S. residents—nearly 1 in 100 adults—lived behind bars, five million others were on probation or parole, more than ten million were booked into jail, and nearly one in three U.S. residents had a criminal record (Kaeble and Glaze 2016, Table 4; PEW Center on the States 2008; Sabol 2014; Subramanian et al. 2016). The scale of confinement now sharply differentiates the United States from comparable countries, where incarceration rates range from a low of 45 per 100,000 residents in Japan to 145 in England and Wales (Walmsley 2015). By 2015, the U.S. incarceration rate had fallen to 670 per 100,000 residents, a drop of nearly 12 percent (Kaeble and Glaze 2016). Still, the United States remains the world’s leading jailer (Wagner and Walsh 2016).