"Eye for an eye" is a theory of punishment derived from a Biblical verse. In essence, when a legal system uses this type of punishment, it has at its basis the belief that the punishment should be equal to the crime and applied to the victim. The simplest manifestation of the "eye for an eye" principle is vengeance after an attack, applied in such a way that the original attacker must endure the same harm that he or she has caused. More commonly, a value might be determined for the injuries suffered by the victim, and the attacker might have to pay the victim that sum. Primarily, this makes sense only in the case of crimes that directly harm people, because more abstract crimes like illegal drug use do not deserve any punishment under the most literal terms of this model.
Originally, the verse that contains the words “eye for an eye” was likely setting up a theory of limitations on vengeance. According to this theory, vengeance may not escalate to a punishment greater than the original crime. While this literal use of the phrase has more or less faded from favor, it is still possible to see literal equal vengeance mediated through a legal system in some areas.
More commonly, legal codes that operate under the principle prescribed by the "eye for an eye" statement offer established fair punishments for certain crimes. A person who kills another person might be put to death, but a person who maims another person might have to pay a fine. It is possible for this principle to be applied not only to bodily injury, but to property loss as well, in which case the necessary compensation is clearer. The beneficiary in these cases is always the person who was wronged or his or her relatives. This principle does not typically punish people for the public good.
The sentiment of the principle of "eye for an eye" is echoed in many legal systems that do not explicitly use those words. Even countries that place value on rehabilitation and correction do not always stray very far from this most basic sentiment in interpersonal respects. When damage is done to a person and the courts decide that compensation must be made, it is almost universally accepted that the remuneration must fit the damage. One of the primary differences in modern law is the recognition of many intangible damages, such as emotional, social, or psychological damages, which can be valued and included in a fair settlement.