The National Defense Service Medal (NDSM) was first intended to be a "blanket campaign medal" awarded to service members who served honorably during a designated time period of when a "national emergency" had been declared during a time of war or conflict.

Originally, awards of the NDSM were restricted to personnel serving on active duty and were retroactive to June 27, 1950 - the date the Korean War began.

A committee appointed by the Department of Defense, which included representatives of all services, met on 27 May 1953 and 3 June 1953 and selected Jones' design for final approval.

[3] Executive Order 12776 of October 8, 1991 extended eligibility for the NDSM to members of the Reserve Components during the period of the Gulf War.

A memorandum from the Office of the Deputy Secretary of Defense, dated April 26, 2002, authorized the reinstatement of the NDSM for all active duty personnel retroactive to September 11, 2001.

This was changed by Executive Order 13293, signed on 28 March 2003, to include Selected Reserve personnel (i.e. drilling reservists) during all periods of eligibility.

There is no time requirement for the medal's issuance, meaning that someone who joins the United States Armed Forces for simply a few days, and then receives an entry-level discharge, would technically be entitled to the NDSM; in practice, however, military clerks will not add the NDSM on a DD Form 214 if the service member performed duty for less than 90 days from the completion of their initial entry training.

Veterans who have this medal so omitted may apply to the military service departments to have the NDSM added to records via a DD Form 215.

[9] Additional awards of the National Defense Service Medal are authorized for members of the military who served in more than one of the eligible time periods.