On September 14, 1814, after witnessing the failed bombardment of Fort McHenry by the British, Francis Scott Key, a Georgetown lawyer and poet, wrote the contrafactum song, "Defence of Fort McHenry," a four stanza poem to be sung to the popular tune "Anacreon in Heaven" by English composer John Stafford Smith which would later be known as the Star-Spangled Banner. Key witnessed the battle after he and John Stuart Skinner, a lawyer, publisher, and prisoner of war exchange officer, had been permitted by President James Madison to negotiate the freedom of Dr. William Beanes, an American physician arrested as a spy. Key and Skinner arrived in the Chesapeake Bay on an American truce ship and boarded the HMS Tonnant, commanded by Admiral Alexander Cochrane. Many days of negotiation eventually led to Barnes' release. Key, Skinner, and Barnes were then transferred to the HMS Surprise and then to their own ship on September 13th. Their ship was tethered to a British ship to prevent them from returning to Baltimore due to the information they had gathered during the negotiation. They witnessed the battle from the deck of their American truce ship. The next morning, on September 14th, Key was inspired to write the poem "Defence of Fort McHenry" when he saw the American flag still flying over Fort McHenry. He wrote the poem in the correct meter to fit the popular English song "Anacreon in Heaven." On their way back to Baltimore, Key showed the poem to Skinner, who is probably the person who eventually passed it along to a young printer's assistant named Samuel Sands, who typeset and printed the poem just a few days later.

The history of Key's poem and the resulting song, "The Star-Spangled Banner," which today traditionally includes only the poem's first stanza, has a complex history and has been the subject of many controversies, including its relative musical difficulty, its alleged origins as a drinking song, anti-British sentiment in the lyrics, and the much-discussed third stanza, which includes the couplet, "No refuge could save the hireling and slave from the terror of flight or the gloom of the grave," in which the slave-holding poet seems to reference formerly enslaved persons who were enticed by the promise of freedom to join the British army's "Corps of Colonial Marines External." It is also possible that Key was referring to the British army as a whole. Hired guns that fought without passion for their cause contrasted with the "freemen" of the American army in the fourth verse. Key may have been mirroring the language of George Robert Chinnery's famous 1810 poem "The Statue of the Dying Gladiator External," which reads, "Haply to grace some Caesar's pageant pride, the hero-slave or hireling-champion died, When Rome, degenerate Rome, for barbarous shows, Barter'd their virtue, glory, and repose, Sold all that freemen prize as great and good, for pomp of death, and theatres of blood!" The same terminology is found in a 1789 issue of the "Gazette of the United States" in which the anonymous author "Americanus" writes, "It is time that this country should begin to trade on its own capital, and not continue to be the slave or hireling of an imperious master." Key never discussed the meaning of his poem or the sources he may or may not have drawn from, so any analysis of the content is necessarily speculative.

Despite these controversies, the Star-Spangled Banner officially became the National Anthem of the United States of America External on March 3, 1931. It was signed into law by President Herbert Hoover. Since then, it has been performed in myriad styles reflecting the ever-changing musical culture of the United States. There have been significant musical changes to the song since its initial publication, which can be seen by comparing sheet music editions provided in this guide and additional stanzas written by poet Oliver Wendell Holmes and sculptor Emma Stebbins during the American Civil War. Just as the United States as a whole must acknowledge the terrible history of slavery and continue to move forward as a unified nation, the Star-Spangled Banner has constantly been evolving since its inception. Classic performances by African-American artists such as Jimi Hendrix, Whitney Houston, and Beyoncé have given audiences a fresh perspective on the anthem in recent times, adding to its legacy. The history of the Star-Spangled Banner is a story that gains a new chapter each time it is performed. Perhaps it is the adaptability of the song that allows it to be a vehicle to simultaneously celebrate our triumphs and acknowledge our painful past while continuing to reflect the spirit of the United States of America.