The U.S. flag flies at half-staff on specific remembrance days on a yearly basis or out of respect for the deaths of U.S. political leaders. By presidential order, the flag flies at half-staff for tragedies or foreign dignitaries' deaths.
The flag always flies at half-staff on Peace Officers Memorial Day on May 15, Patriot Day on September 11 and Pearl Harbor Remembrance Day on December 7. On Memorial Day, the flag only flies half-staff until noon.
If a current or former president dies, the flag flies at half-staff for 30 days following his death. If a current vice president, chief justice of the Supreme Court or speaker of the House of Representatives dies, the flag flies at half-staff for 10 days following his death. If a former vice president dies, the flag flies at half-staff until the person's burial. The same rule applies to the death of a current Supreme Court justice, cabinet member or state governor. If a current congressman dies, the flag flies at half-staff for two days.
The president can order flags to fly at half-staff upon the death of a foreign leader for a specified period of time. For example, flags flew at half-staff for three days following the death of former South African President Nelson Mandela. The president sometimes orders flags to fly at half-staff for tragedies, both domestic and international. For example, following the 2004 Indian Ocean earthquake and tsunami, U.S. flags flew at half-staff for five days.