Treason is an ancient crime, but it fell into disuse in most Western democratic states after World War II. Now it is making a comeback with prosecutions or threatened prosecutions against a new type of enemy—accused terrorists—in the United States, the United Kingdom, and Israel. In the postwar period, commentators wrongly argued that treason would no longer be prosecuted because it is antiliberal, too difficult to prove, unnecessary because modern democracies are stable and secure, and premised on an extinct sense of loyalty to the state. This Article begins by debunking these claims and explaining treason’s recent reappearance. First, democratic states have altered their treason laws, without explicit amendment, to make them akin to other criminal laws. Second, technology has made treason both easier to detect and easier to prove. Third, although the states discussed in this Article are generally stable and secure, states are likely to employ treason prosecutions when they perceive an existential threat (even if one does not actually exist). Finally, the betrayal inherent in treason retains both its power to injure and its power to offend, giving treason as much indignant punch as it has ever had. Treason’s return is thus explainable, but is it a cause for concern? Treason prosecutions may have several potential benefits including reinforcing societal identity and unity, deterring future treasons, providing retribution against the traitor, and clarifying the procedural system under which terrorism should be addressed. But they may also pose dangers, including unduly aggrandizing the threat from terrorism, signaling weakness of the government that chooses to prosecute treason, biasing the criminal case against the defendant, and posing a difficult question about whether treason necessarily deserves the death penalty. Based on a weighing of these factors, this Article concludes by arguing that treason prosecutions are not cause for concern when they are confined to instances in which—like the U.S., British, and Israeli cases discussed in this Article—the threat posed by the terrorist group the traitor supports is akin to that posed by an enemy state.