Blood Law (akin to blood feud) is the English term for the traditional American Indian practice of killing an individual for an offence to another individual or group (tribe, clan, family, etc.). The offences ranged from murder, witchcraft, theft, etc., to insult. If the offending party did not surrender for justice, any member of the offended group could assess the penalty against any member of the offender's group. Traditionally, depending on the character of the offender, death would either be quick (administered by the men), or by slow torture (administered by the women).

The United States discouraged the Blood Law but generally left to the tribes the enforcement of the prohibition unless the murdered victim was non-Indian. Also, the government sometimes stepped in when blood law threatened to lead to war between two different tribes.

Blood Law led to low-level civil war among several of the Five Civilized Tribes during and following their removal to the West. The most noted were the friction between the Lower Creeks and the Upper Creeks and the killings between the John Ross and Ridge factions of the Cherokee Nation; both of which lasted from the 1820s to the American Civil War.

Currently in the United States, only state and federal governments or military courts can impose the death penalty. Justice under Blood Law would be considered revenge killing or summary murder, and also could be an additional aggravating circumstance requiring the death penalty for the crime.

Noted Americans killed under Blood Law

• Elias C. Boudinot
• John Ridge
• Major Ridge
• William McIntosh