In the United States, there are both federal and state laws prohibiting treason. Treason is defined on the federal level in Article III, Section 3 of the United States Constitution as "only in levying War against [the United States], or in adhering to their Enemies, giving them Aid and Comfort." Most state constitutions include similar definitions of treason, specifically limited to levying war against the state, "adhering to the enemies" of the state, or aiding the enemies of the state, and requiring two witnesses or a confession in open court. Fewer than 30 people have ever been charged with treason under these laws.

Treason is the crime of attacking a state authority to which one owes allegiance. This typically includes acts such as participating in a war against one's native country, attempting to overthrow its government, spying on its military, its diplomats, or its secret services for a hostile and foreign power, or attempting to kill its head of state. A person who commits treason is known in law as a traitor.