Between 1777 and 1960 Congress passed several acts that changed the shape, design, and arrangement of the flag and allowed stars and stripes to be added to reflect the admission of each new state. Today the flag consists of 13 horizontal stripes, 7 red alternating with 6 white. The stripes represent the original 13 Colonies and the stars represent the 50 states of the Union. The colors of the flag are symbolic as well; red symbolizes hardiness and valor, white symbolizes purity and innocence, and blue represents vigilance, perseverance, and justice.

Source: PBS