National POW/MIA Recognition Day is an observance that honors whose who were prisoners of war (POW) as well as those who are still missing in action (MIA). It is observed in the United States on the third Friday in September. National POW/MIA Recognition Day was proclaimed by the United States Congress in 1998. It is one of the six national observances when the POW/MIA Flag can be flown. The other five observances are Armed Forces Day, Memorial Day, Flag Day, Independence Day, and Veterans Day.The POW/MIA flag was created by the National League of Families in 1972 and was officially recognized by the Congress in 1990. It is a symbol of concern about United States military personnel taken as POW or listed as MIA.The POW/MIA flag should be no larger than the United States flag. It is typically flown immediately below or adjacent to the national flag as second in the order of precedence. On National POW/MIA Recognition Day, the flag is flown on the grounds of major military installations, veterans memorials, government agencies, federal national cemeteries.In the armed forces, a single table and chair draped with the POW/MIA flag are displayed in mess halls and dining halls. Such installation symbolizes the hope for the return of these who are missing in action.

The POW/MIA flag was created for the National League of Families of American Prisoners and Missing in Southeast Asia and officially recognized by the United States Congress in conjunction with the Vietnam War POW/MIA issue, "as the symbol of our Nation's concern and commitment to resolving as fully as possible the fates of Americans still prisoner, missing and unaccounted for in Southeast Asia, thus ending the uncertainty for their families and the Nation."

The original design for the flag was created by Newt Heisley in 1972 The National League of Families then-national coordinator, POW wife Evelyn Grubb, oversaw its development and also campaigned to gain its widespread acceptance and use by the United States government and also local governments and civilian organizations across the United States.

In 1971, while the Vietnam War was still being fought, Mary Helen Hoff, the wife of a service member missing in action and member of the National League of Families of American Prisoners and Missing in Southeast Asia, recognized the need for a symbol of U.S. POW/MIAs, some of whom had been held captivity for as many as seven years. The flag is black, and bears in the center, in black and white, the emblem of the league. The emblem was designed by Newton F. Heisley, and features a white disk bearing in black silhouette the bust of a man (Jeffery Heisley), watch tower with a guard on patrol, and a strand of barbed wire; above the disk are the white letters POW and MIA framing a white 5-pointed star; below the disk is a black and white wreath above the white motto: "You are not Forgotten." The POW/MIA was flown over the White House for the first time in September 1982. The flag has been altered many times; the colors have been switched from black with white – to red, white and blue – to white with black; the POW/MIA has at times been revised to MIA/POW.

On March 9, 1989, a league flag that had flown over the White House on the 1988 National POW/MIA Recognition Day was installed in the U.S. Capitol rotunda as a result of legislation passed by the 100th Congress. The league's POW-MIA flag is the only flag ever displayed in the rotunda, and the only one other than the Flag of the United States to have flown over the White House. The leadership of both houses of Congress hosted the installation ceremony in a demonstration of bipartisan congressional support.

On August 10, 1990, the 101st Congress passed U.S. Public Law 101-355, recognizing the National League of Families POW/MIA flag and designating it "as a symbol of our Nation's concern and commitment to resolving as fully as possible the fates of Americans still prisoner, missing and unaccounted for in Southeast Asia, thus ending the uncertainty for their families and the Nation." Beyond Southeast Asia, it has been a symbol for POW/MIAs from all U.S. wars.

The flag is ambiguous as it implies that personnel listed as MIA may in fact be held captive. The official, bipartisan, U.S. government position is that there is "no compelling evidence that proves that any American remains alive in captivity in Southeast Asia". The Defense Prisoner of War/Missing Personnel Office (DPMO) provides centralized management of prisoner of war/missing personnel (POW/MP) affairs within the United States Department of Defense and is responsible for investigating the status of POW/MIA issues. As of 29 March 2017, 1,611 Americans remained unaccounted for, of which 1,023 were classified as further pursuit, 497 as no further pursuit and 91 as deferred.

The last loss of the Vietnam War:

CDR Harley H. Hall was the commanding officer of Fighter Squadron 143 onboard the aircraft carrier USS ENTERPRISE. On January 27, 1973 he and his Radar Intercept Officer (RIO), LTCDR Philip A. Kientzler, launched in their F4J Phantom fighter aircraft on an attack mission against North Vietnamese supplies and logistic vehicles 15 miles northwest of Quang Tri, South Vietnam. Hall and Kientzler were under the direction of an OV10 Forward Air Controller (FAC).

CDR Hall's aircraft came under intense anti-aircraft fire while attacking several trucks and was hit. He made an attempt to fly back out to the safety of the sea, but minutes later the aircraft caught fire on the port wing and fuselage.

Both Hall and his co-pilot, LCDR Philip A. Kintzler ejected at 4,000 feet and were seen to land 100 feet apart near a village on an island in the Dam Cho Chua and Cua Viet Rivers. CDR Hall was seen moving about on the ground, discarding his parachute. No voice contact was made with the men, and the probability of immediate capture was considered very high.

Numerous aircraft made several passes over the area for the next several hours and were unsuccessful in observing either of the downed crewmen. Several emergency beepers were heard intermittently the remainder of the afternoon and throughout the night, however, no voice contact was established. Active, organized search and rescue efforts were subsequently terminated.

Only Kientzler was released at Operation Homecoming in 1973. He reported that during parachute descent they received heavy ground fire, at which time he was hit in the leg. He last saw CDR Hall as they touched the ground. When he asked his guards about his pilot, he was told that he was killed by another.

No other returned POW reported having knowledge of Harley Hall, yet the Pentagon maintained him in POW status for over 6 years, and documents were obtained that indicated that he was indeed captured. The Hanoi government claims to have no knowledge of CDR Harley Hall. This former member of the famed Blue Angels flight team remains missing.

Harley Hall was shot down on the last day of the war and was the last Navy air casualty of the Vietnam War. He was the last American to be classified Prisoner of War in the Vietnam War.

Harley H. Hall was promoted to the rank of Captain during the period he was maintained as a prisoner.

In October 2017, state government buildings in Maryland began flying the POW/MIA flag outside.