In the years since September 11, 2001, “Guantánamo” has come to signify the U.S. executive’s policy of detaining persons presumed to have ties to terrorism. The term encompasses the detention on U.S. soil of two U.S. citizens and one Qatari designated “enemy combatants,” as well as the internment of more than 600 non-Americans at offshore sites like Guantánamo. This Article employs the methodology of comparative constitutional law to examine the U.S. policy. It focuses on extraterritoriality and deference, key issues in pending U.S. litigation, yet also explores the scope of detention and the propriety of proposed special tribunals. The Article first demonstrates that no constitutional precedent controls resolution. Then, consistent with the practice of the U.S. Supreme Court in decisions like Lawrence v. Texas, the Article looks to norms drawn from international humanitarian and human rights law to determine whether the detention policy is constitutional. Consultation reveals that U.S. courts have jurisdiction to scrutinize extraterritorial detention, and that the doctrine of deference ought to yield to judicial duty to protect individual rights. Reported conditions of detention and interrogation, as well as the proposal for trial before special tribunals, may violate core guarantees of the U.S. Constitution.