The American flag began with 13 stars and has ended up with 50. In between, Americans have lived under many versions of the national flag.
The first official American flag had 13 stripes, alternating red and white, to represent the 13 Colonies. The early 1776 version had the British Union Jack in the upper lefthand corner. Later that year, the circle of 13 stars replaced the Union Jack. (Whether Betsy Ross created this flag is another matter.) The Second Continental Congress, on June 14, 1777, declared this flag the official flag of the country. (This day is still celebrated as Flag Day.)
American citizens and troops lived and fought under the 13 Colonies flag until 1794, when two more states joined the Union. The flag expanded to include 15 stars and 15 stripes. This was the flag that was flying over Fort McHenry when it was bombed by the British during the War of 1812, inspiring Francis Scott Key to write the Star-Spangled Banner.
Sensing that the nation would expand beyond a normal-sized flag's capability to hold the stripes, Congress in 1818 passed a law designating the number of stripes at 13 but allowing for one star to represent each state of the Union. As more states joined the Union, more stars appeared on the flag. This continued until 1959, when Hawaii became the 50th state. Since 1959, many people have suggested that the flag represent territories that the United States owns as well. For a time, many people pushed for Puerto Rico to become the 51st state. However, the current U.S. flag still has just the 50 stars.