Roper v. Simmons, 543 U.S. 551 (2005), was a landmark decision in which the Supreme Court of the United States held that it is unconstitutional to impose capital punishment for crimes committed while under the age of 18. The 5–4 decision overruled Stanford v. Kentucky, in which the court had upheld execution of offenders at or above age 16, and overturned statutes in 25 states.