543 U.S. 551 (2005)
Roper v. Simmons is a landmark Eighth Amendment decision that constitutionally barred the death penalty for crimes committed by individuals under the age of 18.
Does the Eighth and Fourteenth Amendments' prohibition on cruel and unusual punishments forbid imposing the death penalty on offenders who were under 18 years old at the time they committed capital crimes?
The Eighth Amendment, as incorporated against the States through the Fourteenth Amendment, prohibits punishments that are cruel and unusual as measured by evolving standards of decency that mark the progress of a maturing society. In determining whether a categorical rule is required, the Court looks to (1) objective indicia of national consensus, including legislative enactments and the direction of change; and (2) the Court's own reasoned judgment regarding proportionality and the adequacy of penological justifications. Applying that analysis, the Constitution categorically forbids the execution of offenders who were under 18 at the time of their crimes, overruling Stanford v. Kentucky.
Yes. The Eighth and Fourteenth Amendments categorically prohibit the death penalty for crimes committed by individuals under 18. The Court affirmed the judgment of the Missouri Supreme Court.
Roper is a cornerstone of modern Eighth Amendment proportionality doctrine. It constitutionally fixed the minimum age for capital punishment at 18 and overruled Stanford's contrary rule. Methodologically, it refined the two-step analysis—objective indicia plus independent judgment—and signaled the Court's willingness to credit developmental psychology and comparative practice as corroborative evidence. Substantively, Roper launched a broader juvenile-sentencing jurisprudence that later restricted life-without-parole sentences for juveniles in Graham v. Florida and Miller v. Alabama, and it stands alongside Atkins v. Virginia and, later, Kennedy v. Louisiana as key limits on extreme punishments.