The American military of the 2020s is drawn from a variety of sources authorized by federal and state law. As Section II indicates, throughout American history different laws and policies have governed different parts of the military. The members of the today's American armed forces are drawn from the following sources.

Officers are the product of the service academies—West Point for the Army, Annapolis for the Navy and Marines, the Air Force Academy in Colorado Springs, and the Coast Guard Academy in New London. A substantial portion of the Academy graduates are expected to serve a career in the service of twenty years or more. The best of the graduates will serve as generals and admirals 30 years or more after their academy days.

A second primary source of new officers are the ROTC. These programs are hosted at universities around the country. They appeal to students wishing to attend a civilian university with its wide variety of degrees and, at the same time, to have military training that qualifies them for an officer's commission following graduation. Government support of ROTC programs and students can substantially reduce the cost of a college education.

Other programs allow talented enlisted personnel to advance to an officer's commission. A final path to an officer's commission allows a direct commission from a professional position in civilian life to perform similar military duties. Doctors, lawyers and chaplains are examples.

Enlisted personnel today enter military service through voluntary enlistment. The terms of enlistment typically commit the enlistee to a fixed term of full-time military training and service (usually two to four years) followed by a further period of obligated reserve service. The reserve duty typically requires weekly duty in a reserve unit and several weeks of annual summer service. The reservist is also subject to recall to full-time active duty. After the reservist has completed the obligated term of service, he or she can continue as a reservist for many years, qualifying for retirement benefits at age 60.

A further essential piece of the modern federal military establishment is the National Guard. The Guard combines state government control and national government control of the service member. The states’ National Guards perform a wide variety of missions under the direction of the state governor and legislature. Some duties, such as riot control, mirror national military duties.