The U.S. flag is flown at half-mast for the death of important figures of the U.S. Government and the Governor of a state or territory and to honor the death of foreign dignitaries. The flag is flown half-mast by order of the President, according to the Flag Code.
All military bases, public schools and government buildings must fly flags at half-mast when the President issues an executive order after an important figure dies. When the U.S. flag is flown at half-mast, all flags, including city and state flags, are also flown at half-mast. The tradition of flying the flag at half-mast began in the 17th century.