The 1777 Flag Resolution established the basic stars-and-stripes design of the U.S. flag.
The Second Continental Congress adopted the resolution on June 14, 1777. It specified thirteen alternating red and white stripes and a blue field containing thirteen white stars, representing the thirteen original states. The resolution did not prescribe the exact arrangement of the stars, leaving room for later designs.
The flag's design changed as new states joined the Union. Congress added stars for new states while retaining thirteen stripes, so the current flag has 50 stars but still has 13 stripes. The 15-star flag used from 1795 to 1818 temporarily had 15 stripes as well.
The Flag Resolution is often connected with Betsy Ross, but there is no conclusive historical evidence that she designed or sewed the first official U.S. flag. The resolution itself is the documented congressional action behind the national flag's original legal design.