Capital punishment was widely applied in ancient times; it can be found (c.1750 B.C.) in the Code of Hammurabi. From the fall of Rome to the beginnings of the modern era, capital punishment was practiced throughout Western Europe. The modern movement for the abolition of capital punishment began in the 18th cent. with the writings of Montesquieu and Voltaire, as well as Cesare Beccaria's Essay on Crimes and Punishments (1764). In Great Britain, Jeremy Bentham was influential in having the number of capital crimes reduced in the 18th and 19th cent. Some of the first countries to abolish capital punishment included Venezuela (1863), San Marino (1865), and Costa Rica (1877).

As of 2004, 81 countries had entirely abolished the death penalty, including the members of the European Union. Some other countries retained capital punishment only for treason and war crimes, while in others, death remained a penalty at law, though in practice there had not been any executions for decades. Among countries that retained the death penalty for ordinary crimes were many in the Caribbean, Africa, and Asia. The United States and China were believed to impose capital punishment most frequently.

Since the 1970s almost all capital sentences in the United States have been imposed for homicide. There has been intense debate regarding the constitutionality, effect, and humanity of capital punishment; critics charge that executions are carried out inconsistently, or, more broadly, that they violate the cruel and unusual punishment provision of the Eighth Amendment. Supporters of the death penalty counter that this clause was not intended to prohibit executions. In the 1972 case of Furman v. Georgia, the U.S. Supreme Court ruled that capital punishment as then practiced was unconstitutional, because it was applied disproportionately to certain classes of defendants, notably those who were black or poor. This ruling voided the federal and state death penalty laws then in effect but left the way open for Congress or state legislatures to enact new capital punishment laws, a process that began almost immediately.

In Gregg v. Georgia (1976), the court allowed capital punishment to resume in certain states; in 1977, Gary Gilmore, executed by a firing squad in Utah, became the first to die under the new laws. Today, 35 states and the federal government have reinstituted the death penalty. In 1982, Texas became the first state to execute a prisoner using lethal injection; most executions now employ this method. By 2006, however, concerns over evidence suggesting that some persons had experienced extremely painful executions due to the poor administration of the standard three-drug procedure for lethal injections led several courts to review how the injections were conducted and set stricter standards for them. In 2008 the Supreme Court rejected a challenge to the constitutionality of the three-drug method for lethal injections on the grounds that it could cause extreme pain. The gas chamber, hanging, the firing squad, and, most commonly, the electric chair are still used in some states; Florida's electrocutions, however, were heavily criticized following several grisly malfunctions, and in 2008 Nebraska's supreme court declared the electric chair to be cruel and unusual punishment. Texas easily leads all other states in the number of executions carried out, although it imposes the death penalty in murder cases less often than the national average.

In recent years, the Supreme Court has made it more difficult for death-row prisoners to file appeals, but it also sometimes has overturned death sentences or restricted their imposition. In 1988 the Court barred the execution of juveniles who were younger that 16 when they committed a crime; a 2005 decision extended this to offenders under the age of 18. In 2002 the Court barred the execution of mentally retarded offenders, overturning its 1989 ruling on the matter. Also in the same year the Court ruled that the death penalty must be imposed through a finding of a jury and not a judge.

Studies continue to show disparities in the imposition of capital punishment (it is most likely to be imposed if the victim was white and the defendant is black, but is least likely to be imposed if both victim and defendant are black), and criticism of the practice in the United States and abroad has been increasing markedly. The use of DNA fingerprinting to exonerate persons falsely convicted of rape and other crimes also has led to calls, in some instances by supporters of the death penalty, for the reexamination of the use of an ultimately irreversible sentence, and several states have appointed commissions to examine the issue. In 2002, in a surprising and controversial move, Illinois governor George Ryan commuted the sentences of all the state's death row inmates, saying that conviction errors and unfair imposition make capital punishment arbitrary and capricious.