After the terrorist operations of September 11, 2001, President George W. Bush authorized the creation of military tribunals to try individuals who offered assistance to the attacks on New York City and Washington, D.C. The military order issued by President Bush closely tracks the model established by President Franklin D. Roosevelt for a military tribunal appointed in 1942 to try eight German saboteurs. In Ex parte Quirin (1942), the Supreme Court unanimously upheld the jurisdiction of Roosevelt's tribunal (also called "military commission"). This report summarizes the types of military tribunals that have functioned from the Revolutionary War to the present time, explaining the legislative enactments that have guided these tribunals and the judicial decisions that have reviewed their constitutionality. One of the principal methods of legislative control over military trials, including tribunals, are the Articles of War that Congress enacts into law. The Constitution vests in Congress the power to "constitute Tribunals inferior to the supreme Court," to "make rules for the Government and Regulation of the land and naval Forces," and to "define and punish Piracies and Felonies committed on the high Seas, and Offences against the Law of Nations." By enacting Articles of War, Congress defined not only the procedures but also the punishments to be applied to the field of military law. At various times, executive officials have claimed that the President has authority under the Constitution to create military tribunals and does not depend on statutory authorization. The Supreme Court has never accepted that argument. Instead, it looks for implied or express statutory authority when upholding military tribunals. On a number of occasions, federal courts have expressed concern that military tribunals enable an administration to exercise all three powers of government --- legislative, executive, and judicial --- and that the concentration of those powers threatens individual rights and liberties.