The first private prison in the US opened in 1984. Over the next three decades, the imprisoned population increased by 194% while the country’s overall population increased by only 36%. This column examines the relationship between these two events, asking whether the growth of the private prison industry contributed to climbing incarceration rates. It concludes that private prisons moderately increased sentence lengths but not the likelihood of conviction, and finds no evidence that private prisons directly influenced judges or exacerbated existing racial biases in the judicial system.