Since 1980, the number of people incarcerated in the United States has more than quadrupled; the nation now has the largest prison population in the world. The criminal justice system is not only inefficient, it is also ineffective. Reducing mass incarceration and reforming the criminal justice system is bringing together an unexpected and diverse coalition, including Republicans and Democrats, social liberals and economic conservatives. Our Deep Dive starts with an exploration of the fascinating research on criminal justice with key researchers, practitioners, and reformers. We also offer insights to a bipartisan effort to reform our prison system nationally. What does our prison system look like today? What needs to change — and why?