The Poem
"The Star-Spangled Banner" is the National Anthem of the United States of America.  The lyrics come from the poem "Defence of Fort McHenry" written by Francis Scott Key in 1814 after seeing the bombardment of Fort McHenry by Royal Navy ships during the War of 1812 in Chesepeake Bay.
The Inspiration
During the rainy night of September 13th, 1814, Francis Scott Key witnessed the bombardment of Fort McHenry while being held captive aboard a British Flagship.  The Fort's smaller storm flag continued to fly through the bombardment of shells and rockets.  Once the fighting had stopped, it would not be known until dawn as to the fate of Fort McHenry.  At dawn, Key saw that the storm flag had been lowered, and the larger flag had been raised.  The flag is now known as the 15 star, 15 stripe "Star-Spangled Banner" flag.
Official Use
"The Star-Spangled Banner" was first officially recognized for use by the Navy in 1889 and by president Woodrow Wilson in 1916.
In 1931, under President Herbert Hoover, it was made the official National Anthem of the United States of America by a Congressional Resolution.
The Flag Today
The "Star-Spangled Banner" flag is now on display at the National Museum of American History.  It was restored in 1914 and again in 1998 as part of an ongoing conservation program.
The Star-Spangled Banner
Our National Anthem
Oh, say can you see by the dawn's early light
What so proudly we hailed at the twilight's last gleaming?
Whose broad stripes and bright stars thru the perilous fight,
O'er the ramparts we watched were so gallantly streaming?
And the rocket's red glare, the bombs bursting in air,
Gave proof through the night that our flag was still there.
Oh, say does that star-spangled banner yet wave
O'er the land of the free and the home of the brave?

On the shore, dimly seen through the mists of the deep,
Where the foe's haughty host in dread silence reposes,
What is that which the breeze, o'er the towering steep,
As it fitfully blows, half conceals, half discloses?
Now it catches the gleam of the morning's first beam,
In full glory reflected now shines in the stream:
'Tis the star-spangled banner! Oh long may it wave
O'er the land of the free and the home of the brave!

And where is that band who so vauntingly swore
That the havoc of war and the battle's confusion,
A home and a country should leave us no more!
Their blood has washed out their foul footsteps' pollution.
No refuge could save the hireling and slave
From the terror of flight, or the gloom of the grave:
And the star-spangled banner in triumph doth wave
O'er the land of the free and the home of the brave!

h! thus be it ever, when freemen shall stand
Between their loved home and the war's desolation!
Blest with victory and peace, may the heav'n rescued land
Praise the Power that hath made and preserved us a nation.
Then conquer we must, when our cause it is just,
And this be our motto: "In God is our trust."
And the star-spangled banner in triumph shall wave
O'er the land of the free and the home of the brave!