Every day is a great occasion on which to fly the American
flag. But according to the United States Code Title 4, Chapter
1, Section 6d, there are some special occasions specifically
designated by the government as days on which the American
flag should be flown.
and special occasions
The American flag should also be flown on designated election
days or the anniversary of a state's admittance into the Union.
date of admittance to the Union
In addition, The President of the United States has the
authority to designate a special occasion on which the flag
should be flown, such as September 11, 2001 and the 30 days
after, when flags were flown at half-staff by executive order.