The United States flag has 13 horizontal stripes.
The stripes alternate red and white and represent the thirteen British colonies that declared independence and became the original states. The blue canton contains stars representing the states in the Union, so the stripes and stars symbolize different parts of the country's history.
The first national flag legislation, the Flag Resolution of June 14, 1777, specified thirteen alternating red and white stripes and thirteen white stars on a blue field. Congress later increased the flag to 15 stripes when Vermont and Kentucky joined the Union in 1791 and 1792.
In 1818, Congress restored the number of stripes to 13 while establishing that a new star would be added for each new state. This is why the modern flag still has 13 stripes but currently displays 50 stars. Flag designs changed several times as the country expanded.