The United States Flag, specifically, is displayed at half staff to signify that the country as a whole is in mourning. These special mourning periods are determined by the order of the US President for national memorials, and can also be ordered by the governor of a state, territory, or possession who can direct the U.S. flag to be flown at half staff within their jurisdiction to memorialize an important citizen to their area. When the US President orders the flag to be displayed at half mast, the direction is carried out at all buildings, grounds, and naval vessels of the Federal Government including abroad at US embassies, government facilities, military facilities, and military vessels.

Leaders of specific government agencies and departments of the U.S. government can also direct the U.S. flag to be flown at half staff on ships, buildings, and grounds within their authority. The duration varies from a few days (usually until sunset on the day of the burial) to 30 days, according to the deceased person's position.

On March 1, 1954, President Dwight Eisenhower issued a proclamation, outlining a set of standard guidelines which outline rules for the proper occasions that the US Flag should be displayed at half staff, which are listed below:

• Upon the death of any current or former President of the United States, the flag is to be flown at half staff for thirty days from the day of death.

• Upon the death of The Vice President, Chief Justice or a retired Chief Justice of the United States, or the Speaker of the House of Representatives, the flag is to be flown at half staff for ten days from the day of death.

• Upon the death of an Associate Justice of the Supreme Court, a member of the Cabinet, a former Vice President, the President pro tempore of the Senate, the Majority Leader of the Senate, the Minority Leader of the Senate, the Majority Leader of the House of Representatives, or the Minority Leader of the House of Representatives, the flag is to be flown at half staff from the day of death until burial.

The protocol was further expanded in 1969 to include more circumstances where the flag should or could be flown at half mast:

• Upon the death of any United States Senator, Representative, Territorial Delegate, or the Resident Commissioner from the Commonwealth of Puerto Rico, the flag is to be flown at half staff on the day of death and the following day.

• Upon the death of the Governor of a State, Territory, or possession, the flag is to be flown at half staff on the day of death until burial.

• The President can order the flag to be displayed at half staff if any other important person dies at the President's discretion.

• The leadership of departments and agencies of the Government may direct the flag of the United States be flown at half-staff on buildings, grounds, or naval vessels under their jurisdiction at their discretion.

In addition to the circumstances outlined above, there are four US Flag holidays each year, when the American Flag should be displayed at half staff.

• May 15 - Peace Officer's Memorial Day

• Last Monday in May - Memorial Day

• Sep 11 - Patriot Day

• Dec 7 - Pearl Harbor Remembrance Day

The proper protocol for displaying a flag at half staff is to briskly raise the flag to the top of the staff before lowering it slowly and ceremoniously to the half-staff position. Although there are no laws governing the half-staffing of flags at private homes, grounds, organizations, and vessels, most citizens follow the flag display customs used by the US federal government.

It is proper etiquette to display the American Flag from sunrise to sunset. In the event that one chooses to display the US flag 24 hours a day, the flag should be illuminated during the night.