Missouri v. Lewis was a United States Supreme Court case that addressed the issue of whether a state could impose a death penalty on a defendant who was under the age of 18 at the time of the crime. The case involved a defendant, Lewis, who was convicted of murder in Missouri and sentenced to death. The Supreme Court held that the state of Missouri could not impose the death penalty on Lewis because he was under the age of 18 at the time of the crime. The Court reasoned that the Eighth Amendment's prohibition against cruel and unusual punishment applied to minors, and that the death penalty was a form of cruel and unusual punishment. The Court also noted that the state of Missouri had not provided any evidence that Lewis was mature enough to understand the consequences of his actions. As a result, the Court held that the death penalty could not be imposed on Lewis.

In Missouri v. Lewis, the United States Supreme Court was asked to decide whether a state could prosecute an individual for murder if they had already been acquitted of the same crime in another state. The majority opinion held that states were not allowed to do so due to double jeopardy protections under the Fifth Amendment. However, Justice Field dissented from this ruling and argued that since each state is sovereign over its own criminal laws, it should be able to try individuals for crimes committed within its borders regardless of what other states have done with respect to those same crimes. He further noted that allowing one state's acquittal or conviction on a particular charge would bind all other states in their prosecution decisions regarding similar charges against the same defendant - something he felt was inappropriate given each state's autonomy when it comes to criminal law enforcement matters.