Sumner v. Shuman, 483 U.S. 66 (1987), was a case in which the Supreme Court of the United States held that a mandatory death penalty for a prison inmate who is convicted of murder while serving a life sentence without possibility of parole is unconstitutional.

[3] In a 6–3 decision, the Supreme Court held that the mandatory imposition of the death penalty on inmates convicted of murder while serving a life sentence without the possibility of parole was unconstitutional.

Writing for the majority, Justice Harry Blackmun reasoned that the Eighth Amendment requires individualized sentencing in capital cases, allowing for the consideration of mitigating factors related to the defendant's character or the circumstances of the crime.

The Court cited its previous decisions in Woodson v. North Carolina, 428 U.S. 280 (1976), and Lockett v. Ohio, 438 U.S. 586 (1978), which had invalidated mandatory death penalty statutes for similar reasons.

As a result, the Court held that the Nevada statute violated the Constitution by denying Shuman the opportunity to present mitigating evidence before a jury or judge to potentially avoid a death sentence.