In historical legal systems, an outlaw is declared as outside the protection of the law. In pre-modern societies, this takes the burden of active prosecution of a criminal from the authorities. Instead, the criminal is withdrawn all legal protection, so that anyone is legally empowered to persecute or kill them. Outlawry was thus one of the harshest penalties in the legal system, since the outlaw had only himself to protect himself, but it also required no enforcement on the part of the justice system. In early Germanic law, the death penalty is conspicuously absent, and outlawing is the most extreme punishment, presumably amounting to a death sentence in practice.

The concept is known from Roman law, as the status of homo sacer, and persisted throughout the Middle Ages. It was only in the modern period that the principle of habeas corpus was established, requiring that criminals must be judged in person by a court of law before they can legally be punished.

In the common law of England, a "Writ of Outlawry" made the pronouncement Caput gerat lupinum ("Let his be a wolf's head," literally "May he bear a wolfish head") with respect to its subject, using "head" to refer to the entire person and equating that person with a wolf in the eyes of the law: Not only was the subject deprived of all legal rights of the law being outside of the "law", but others could kill him on sight as if he were a wolf or other wild animal.