Life without parole sentencing refers to laws, policies, and practices concerning lifetime prison sentences that also preclude release by parole. While sentences to imprisonment for life without the possibility of parole have existed for more than a century in the United States, over the past four decades the penalty has emerged as a prominent element of U.S. punishment, routinely put to use by penal professionals and featured regularly in public discourse. As use of the death penalty diminishes in the United States, life without parole serves as the ultimate punishment in more and more U.S. jurisdictions. The scope with which states apply life without parole varies, however, and some states have authorized the punishment even for nonviolent offenses. More than a punishment serving purposes of retribution, crime control, and public safety, and beyond the symbolic functions of life without parole sentencing in U.S. culture and politics, life without parole is a lived experience for more than 50,000 prisoners in the United States. Life without parole’s increasing significance in the United States points to the need for further research on the subject—including studies that directly focus on how race and racial prejudice factor in life without parole sentencing, studies that investigate the proximate causes of life without parole sentences at the state and local level, and studies that examine the similarities and differences between life without parole, the death penalty, and de facto forms of imprisonment until death.