The Continental Congress adopted the thirteen-star U.S. flag on June 14, 1777.
The Flag Resolution specified thirteen alternating red and white stripes and thirteen white stars on a blue field. Congress described the stars as representing a new constellation. The thirteen elements represented the thirteen United States, formerly the colonies that had declared independence from Britain.
The resolution did not prescribe one arrangement for the stars. Early flags used circles, rows, squares, and other patterns, and the familiar Betsy Ross arrangement is only one later design tradition. There is also no conclusive evidence that Betsy Ross designed the first official flag.
The flag continued to change as new states joined the Union. In 1795, Congress increased both the stars and stripes to fifteen for Vermont and Kentucky. The Flag Act of 1818 restored the stripes to thirteen and established the practice of adding a star for each new state. The current fifty-star flag became official on July 4, 1960, after Hawaii joined the Union.