The Selective Service Act passed Congress in May 1917, requiring all American men between the ages of 21 and 30 to register for military service, or the draft. It was the first draft registration since the Civil War, but unlike the Civil War, men could no longer pay someone to take their place in the military. Draft registration cards were completed by more than 24 million men in the United States during World War I. "Aliens" or residents who were not citizens, were required to register but not required to serve.

In July 1917, the U.S. government conducted a draft lottery. Draft numbers were chosen randomly from a large glass bowl. The men whose numbers were chosen were required to meet with a draft board, who decided whether or not that man would be eligible for military service. In 1918, the United States extended the draft ages to men between 18-45.