The draft was essential in raising the large numbers of men needed. Voluntary enlistment had not produced the needed number. Establishment of a draft was controversial in both the U.S. and Britain. President Wilson proposed the American draft and characterized it as necessary to make "shirkers" play their part in the war. This argument won over key swing votes in Congress.

Aliens residing in the United States were required to register for the draft although they were not subject to induction into the American military. In some frontier locations, such as Alaska, aliens formed the majority of registrants.

Men already on active duty in the military were excluded from draft registration. Because some men who completed draft cards later voluntarily enlisted, it is difficult to determine exactly how many active duty military men never completed a draft card, but the number would be between 300,000 and 600,000. Registration of eligible men has been determined to be close to 100%, which means that about 98% of adult men under age 46 living in the U.S. in 1917-18 completed registration cards.

During this 1917-18 period, an especially virulent influenza pandemic killed mostly young adults. As this influenza situation affected draft registration, some men under age 21 were dead by the time it came their turn to register in 1918.

In practice, only three draft lotteries were held. Those registrants whose numbers were drawn were then subject to induction unless they could show good cause why they should not be inducted. The three registration days for these lotteries were held:

a) June 5, 1917 for persons born 1886-1896. About 10 million men registered on this date. Those who completed this registration card listed birth date, birth location and other information. Because of specific opposition from Congress, 18-20 year olds were initially exempt.

b) June 5, 1918 for persons born 1896-97. This group of about one million men who had recently become old enough to be drafted during the preceding year registered on this date. Those who completed this registration card listed birth date, birth location and other information. They also listed their father's birth location. About half of these men had only vague information about their father's birth location.

c) September 12, 1918 for persons born 1873-1886 and 1897-1900. Almost 14 million men registered on this date. Those who completed this registration card listed birth date, but not birth location. A detailed listing of the address of next of kin on this card, however, can provide valuable information, especially in cases of recent immigrants.

In addition, a tiny number of men who turned 21 in August, 1918, registered in that month.

A small number of dates on the cards vary from these three registration dates. These probably represent errors or registration filings by persons who were prevented from registering on the designated dates. A few men were allowed to register early due to hardship situations, including a situation where they were scheduled to be traveling or out-of-town on registration day. This was so interpreted in New York, for example, to allow the wealthy business executive John D. Rockefeller Jr. to register early because of a business trip. On the designated registration days, businesses and schools closed down in most communities. Saloons closed in most states. Registration started at 7 or 7:30 a.m. and lasted until late at night. In New York City, boat horns were blown to announce the start of registration, and in Provo, Utah whistles performed a similar function. In Vicksburg, Mississippi, church bells and whistles were used. In Jackson, Mississippi, cannons at the old state capitol building were to have been fired at the start of registration, but organizers had difficulty finding gunpowder. Similar noise-making events occurred across the country.

Family members often came with the registrant to the registration site.

Patriotic parades were held on the first registration day, as in Spanish Fork, Utah, where registrants were included in the automobile parade. In Memphis, Tennessee, 25,000 marched in a loyalty parade. General Wood addressed parade participants in Birmingham, Alabama. In Hinds Co., Mississippi, a regimental band went from one registration place to another, playing patriotic music for the registrants.

On the first registration date, it was intended that the tally of registrants was to be wired that night to Washington, but most boards were not able to meet this goal because they were overwhelmed with the task of processing registrants. Some boards had to call for additional volunteer staff due to the large number of registrants. In Salt Lake City, a deputized registrar made a tour of the hospital on registration day registering men unable to leave the hospital. These hospitalized men could also have appointed someone to obtain the registration card prior to registration day from the city or county clerk.

Volunteer interpreters were recruited and assisted with the registration of those who did not speak English. New York City reported a shortage of interpreters, especially of those who spoke uncommon languages.

In the vast majority of cases, volunteer staff at the local office filled in the information on the card, and the registrant then signed his name. Instructions for filling in each question on the card were posted for all to read at each registration site, and the local newspapers sometimes printed copies of sample cards in the days prior to registration. One photo taken in New York City shows an all-female staff at a long table interviewing seated registrants. Many of these women were teachers from the city schools, which had closed for the day.

A few of the microfilmed cards are actually copies of the signed originals, and the signatures on these copies thus exhibit the same handwriting as the rest of the card. One microfilmed version of the cards of the 35 boards in Detroit, Michigan seem to all be copies which have been alphabetized into a unified set combining all the Detroit boards into one file.

When the draft registration district was densely populated, as in each district in New York City, then only one site was typically available for registration. More commonly, multiple sites were made available in each county's single district, often corresponding to voting sites.