This March 2015 report addresses a critical question: What caused the American crime decline? Was it incarceration? Was it policing? Or was it something else? This groundbreaking empirical analysis from the Brennan Center shows that, on examination, the easy answers do not explain incarceration’s effect on crime. This report presents a rigorous and sophisticated empirical analysis performed on the most recent, comprehensive dataset to date. The authors conclude that incarceration had relatively little to do with the crime decline. They find that the dramatic increases in incarceration have had a limited, diminishing effect on crime. And they have quantified those minimal benefits. At today’s high incarceration rates, continuing to incarcerate more people has almost no effect on reducing crime.