A stand-your-ground law, sometimes called "line in the sand" or "no duty to retreat" law, provides that people may use deadly force when they reasonably believe it to be necessary to defend against certain violent crimes (right of self-defense). Under such a law, people have no duty to retreat before using deadly force in self-defense, so long as they are in a place where they are lawfully present. The exact details vary by jurisdiction.

The alternative to stand your ground is "duty to retreat". In jurisdictions that implement a duty to retreat, even a person who is unlawfully attacked (or who is defending someone who is unlawfully attacked) may not use deadly force if it is possible to instead avoid the danger with complete safety by retreating.

Even areas that impose a duty to retreat generally follow the "castle doctrine", under which people have no duty to retreat when they are attacked in their homes, or (in some places) in their vehicles or workplaces. The castle doctrine and "stand-your-ground" laws provide legal defenses to persons who have been charged with various use of force crimes against persons, such as murder, manslaughter, aggravated assault, and illegal discharge or brandishing of weapons, as well as attempts to commit such crimes.

Whether a jurisdiction follows stand-your-ground or duty-to-retreat is just one element of its self-defense laws. Different jurisdictions allow deadly force against different crimes. All American states allow it against deadly force, great bodily injury, and likely kidnapping or rape; some also allow it against threat of robbery and burglary.

A 2020 RAND Corporation review of existing research concluded: "There is supportive evidence that stand-your-ground laws are associated with increases in firearm homicides and moderate evidence that they increase the total number of homicides."