In the United States, life imprisonment is the most severe punishment provided by law in states with no valid capital punishment statute, and second-most in those with a valid statute. According to a 2013 study, one of every nine prison inhabitants of the U.S. were imprisoned for life .

American case law and penology literature traditionally divides life sentences into "determinate life sentences" or "indeterminate life sentences". (At p. 272.) The latter indicates the possibility of an abridged sentence, usually through the process of parole. For example, a sentence of "15 years to life" or "25 years to life" is called an "indeterminate life sentence", while a sentence of "life without the possibility of parole" or "life without parole" (LWOP) is called a "determinate life sentence".In re Jeanice D., 28 Cal. 3d 210 (1980) ("25 years to life" is indeterminate life sentence implying that minor convicted of first-degree murder was eligible for commitment to the California Youth Authority, rather than determinate life sentence requiring incarceration in regular adult prison). West Virginia uses the unique terms "life with mercy" and "life without mercy", respectively, for these two categories.

The first category are "indeterminate" in that the true length of each prisoner's sentence is not determined up front by the sentencing court, but will depend upon when the prisoner can convince the state parole board of their rehabilitation after serving the minimum number of years provided for in the sentence. (At p. 273.) The ability of most prisoners to earn good conduct time sentence reductions further complicates the calculation of when a particular prisoner will actually get to first meet the parole board. The second category are "determinate" in that it is expressly determined by the sentencing court up front that the prisoner will never have the chance to see the parole board. Therefore, criminals given a determinate life sentence will typically die in prison, without ever being released. If a life without parole sentence is imposed, executive branch government officials (usually the state governor) may have the power to grant a pardon, or to commute a sentence to time served, effectively ending the sentence early.

Many U.S. states offer parole after a decade or more has passed, but in California, people sentenced to life imprisonment can normally apply for parole after seven years. Florida leads the country with nearly one quarter of the nation's LWOP prisoners, more than California, New York and Texas combined.

History In the 1860s, reformation became favored over penitence in American penology, with the role of prisons seen as reforming prisoners, who were imprisoned until reform was achieved. The concepts of parole and indeterminate sentencing were regarded as forward-looking in the 1870s. The initial concept of parole came from the idea that prisoners began their path to rehabilitation during their sentence, and their successful rehabilitation could be recognizable by a parole board. The importance was placed on eradicating crime and having prisoners deemed ready to enter society as soon as possible. However, the ideals were not as successful as had been hoped. Crime was not eradicated, reformatories had the same problems as prisons on politicization and underfunding, and indeterminate sentencing became undermined by prisoners, who quickly found that it was possible to "beat the system" by pretense to get a better chance of winning parole. Many were soon back in custody. Similarly, prison authorities could twist it to their advantage by using those granted parole or probation to spy on and actively help to imprison other people, or sometimes by selectively denying parole. However, the biggest cause of the reformatories' failure to live up to expectations was that despite the enthusiasm of reformers and Zebulon Brockway's call for an end to vengeance in criminal justice, those within the prison environment, both inmates and guards alike, continued to conceive of prison as a place of retribution.A. E. Weiss, Prisons, A System in Trouble (1988), pp. 29–30.

Schick's case and life imprisonment without parole In 1954 (November 28), Master Sergeant Maurice L. Schick was convicted by military court-martial of the murder of nine-year-old Susan Rothschild at Camp Zama in Japan (Tokyo).SOLDIER ADMITS SLAYING; Sergeant in Tokyo Confesses to Killing 9-Year-Old Girl, New York Times. November 28, 1953 The soldier admitted the killing stating he had a sudden "uncontrollable urge to kill something quickly and quietly” and had chosen his victim "just because she was there."Army Seargreant Confesses. November 28, 1953. San Francisco Examiner

Schick was sentenced to death. Six years later, the case was forwarded to President Dwight Eisenhower for final review. He exercised his right of executive clemency to commute Schick's death sentence to confinement with hard labor for the term of his natural life, with the express condition that he "shall never have any rights, privileges, claims or benefits arising under the parole and suspension or remission of sentence laws of the United States."

In 1971, Schick began a legal challenge against his whole life sentence. The appeal eventually reached the U.S. Supreme Court in 1974. It examined the constitutional basis of the punishment: life imprisonment without parole.Schick v. Reed, 419 U.S. 256 (1974). Had Schick been given an ordinary life sentence, he would have been eligible for parole in 1969.

Although Schick's sentence was given only cursory mention, the court concluded a whole life sentence was constitutional.J. H. Wright, Jr., "Life Without Parole: An Alternative to Death or Not Much of a Life At All?" 43 Vanderbilt Law Review 529, 535 (1990). Schick, together with only five other federal prisoners who were still ineligible for parole at the time, was made eligible for parole by a separate pardon from President Gerald Ford in 1977. He was paroled in 1979 and died a free man in Palm Beach, Florida in 2004.

Despite the Schick opinion's lack of thorough analysis on life imprisonment without a chance of parole, an imposing amount of precedent has developed based upon it.Wright, supra, at p. 536. After Furman v. Georgia,408 U.S. 238 (1972). the constitutionality of life imprisonment without parole as an alternative to the death penalty received increased attention from lawmakers and judges.

Such penalties predate Schick.see Green v. Teets, 244 F2d 401 (9th Cir. 1957); United States v. Ragen, 146 F2d 349 (7th Cir.), cert denied, 325 U.S. 865 (1945); and State v. Dehler, 257 Minn. 549, 102 N.W.2d 696 (1960). One early American case was Ex parte Wells (1856);18 How. 307 (1856). Wells was convicted of murder in 1851 and sentenced to be hanged. On the day of his execution, President Millard Fillmore gave him a conditional pardon commuting his sentence to "imprisonment for life in the penitentiary at Washington." Wells appealed the conditions of his pardon, but the sentence was upheld with no discussion by the majority of the purpose of the substituted punishment.

Minors A few countries worldwide have allowed for minors to be given lifetime sentences that have no provision for eventual release. Countries that allow life imprisonment without a possibility of parole for juveniles include Antigua and Barbuda, Cuba, Dominica, Israel, Nigeria, Saint Vincent and the Grenadines, the Solomon Islands, Sri Lanka, Tanzania and the United States. Of these, only the U.S. currently has minors serving such sentences. The University of San Francisco School of Law's Center for Law & Global Justice conducted international research on the use of the sentence of life without parole for juveniles, and has found no cases outside the U.S. in which the sentence is actually imposed on juveniles.See C. de la Vega & M. Leighton, Sentencing our Children to Die in Prison: Global Law and Practice, 42 U.S.F. Law Review 983, 989 (2008). The research was conducted in 2007, updated in 2008 to clarify that Tanzania, South Africa and Israel do not allow juvenile life without parole, and cited by the U.S. Supreme Court in 2010 in Graham v. Florida. The University of San Francisco Center for Law & Global Justice continues to monitor international juvenile sentencing laws and practices. As of 2009, Human Rights Watch has calculated that there are 2,589State Distribution of Youth Offenders Serving Juvenile Life Without a chance of Parole (JLWOP) Human Rights Watch, October 2, 2009. youth offenders serving life without parole in the U.S."The Rest of Their Lives: Life without Parole for Child Offenders in the United States", Human Rights Watch, May 1, 2008

In the U.S, juvenile offenders started to get life without parole sentences more frequently in the 1990s due to John J. DiIulio Jr's. Teenage Superpredator Theory.

In 2010, the U.S. Supreme Court ruled that sentencing minors to automatic sentences of life without a chance of parole for crimes other than those involving a homicide (generally, first-degree murder, and usually with aggravating factors or accompanying felonies) violated the Eighth Amendment's ban on "cruel and unusual punishments", in the case of Graham v. Florida.Graham v. Florida, 130 S. Ct. 2011 (2010). In finding that the U.S. Constitution prohibits as cruel and unusual punishment a life without parole sentence for a juvenile in a non-homicide case, the U.S. Supreme Court stated that "the overwhelming weight of international opinion against" juvenile life without a chance of parole "provide[s] respected and significant confirmation for our own conclusions".Graham v. Florida, supra, 130 S. Ct. at 2034 (concluding that juvenile life without parole is unconstitutional for non-homicide crimes). In 2012, in the case of Miller v. Alabama, the Court considered whether to ban the automatic use of it completely as a sentence for minors. The Court had already judged the death penalty unconstitutional for minors in 2005. In June 2012, the Court ruled that it could never be automatically used as a sentence for a minor (under 18), although the Court left room for it as a sentence that can eventually be given (for now) in certain first-degree murder cases once the judge has taken mitigating circumstances and other factors into account. The U.S. practice of sentencing juveniles to life imprisonment without a possibility of parole violates international standards of justice, as well as treaties to which the U.S. is a party. Each state must ensure that its criminal punishments comply with the United States' international treaty obligations: The International Covenant on Civil and Political Rights; the oversight Committee instructed the U.S. to: "ensure that no such child offender is sentenced to life without parole [and] adopt all appropriate measures to review the situation of persons already serving such sentences". The United Nations Convention Against Torture; the oversight Committee warned the U.S. that juvenile life sentences without a possibility of parole could constitute "cruel, inhuman or degrading treatment or punishment" for youth. The oversight body of the Committee on the Elimination of Racial Discrimination found that juvenile life without a chance of parole is applied disproportionately to black minors, and the U.S. has done nothing to reduce what has become pervasive discrimination. The Committee recommended that the U.S. discontinue the use of this sentence against persons under the age of eighteen at the time the offense was committed, and review the situation of persons already serving such sentences and in 2016, in the case of Montgomery v. Louisiana, the Supreme Court ruled that Miller v. Alabama was to be applied retroactively to offenders convicted before 2012.