Treason, the committing of disloyal acts against the government to which the offender owes allegiance. A person who commits treason is called a traitor. In many societies, treason is considered the gravest crime a person can commit.

The United States Constitution defines treason as follows:

Treason against the United States shall consist only in levying war against them, or in adhering to their enemies, giving them aid or comfort. No person shall be convicted of treason unless on the testimony of two witnesses to the overt act, or on confession in open court.

—Article III, Sec. 3

This crime was specifically defined in the Constitution to prevent the charge of treason from being used by unscrupulous persons as a weapon against their opponents. Treason is punishable by death or imprisonment; however, because of the restrictive interpretation of this crime, few cases of treason against the United States have been prosecuted, and no one has been executed.

Treason against a state government is a separate offense; it is defined and punishable by state law. John Brown, the abolitionist who conducted a raid on Harpers Ferry, Virginia (now West Virginia), is believed to be the only person executed for treason against a state.

Treason against a sovereign or head of state is sometimes called a high treason to distinguish it from treasonable acts against a country itself.