In the United States, Congress and the president must authorize the compulsory enlistment of citizens into military service. The first such U.S. military draft was authorized in 1863, during the Civil War. Additional drafts were authorized during the Spanish-American War, World Wars I and II, the Korean War and the Vietnam War. The most recent congressional authorization to draft inductees into the U.S. military expired on June 30, 1973 and has not been reinstated.

Selective Service

While the United States currently has an all-volunteer military, all male U.S. citizens are required to register for with the Selective Service System within 30 days of their 18th birthday. Non-citizen men between the ages of 18 and 25 who reside in the U.S. must also register. Congress made significant changes to the rules which govern military drafts in 1971. Should the U.S. Congress and president approve a draft today, inductees would be chosen by lottery from men aged 18 to 25 and, unlike the Vietnam-era draft, students would only be able to defer their eligibility for the draft until the end of the current semester.