Over a decade ago, researchers, policymakers, journalists, and individuals and family members harmed by prisons and jails helped define American mass incarceration as one of the fundamental policy challenges of our time. In the years since, policymakers and voters in red, blue, and purple jurisdictions have advanced criminal justice reforms that safely reduced prison and jail populations, expanding freedom and opportunities to tens of millions of Americans. After nearly forty years of uninterrupted prison population growth, our collective awareness of the costs of mass incarceration has fundamentally shifted–and our sustained efforts to turn the tide have yielded meaningful results.