The original United States flag adopted by Congress in 1777 had 13 stripes.
The Flag Resolution of June 14, 1777, specified thirteen alternating red and white stripes and thirteen white stars on a blue field. The stripes represented the thirteen states or former colonies united in the Revolution.
The design later changed when Vermont and Kentucky joined the Union. The flag temporarily had fifteen stripes and fifteen stars, but Congress returned the stripes to thirteen in 1818 while continuing to add a star for each new state.
The modern flag therefore has thirteen stripes and fifty stars. The stripes preserve the symbolism of the original thirteen colonies, while the stars represent the current number of states. June 14 is observed as Flag Day in the United States.