What we know fondly as the "Stars and Stripes" was adopted by the Continental Congress as the official American flag on June 14, 1777, in the midst of the Revolutionary War. Colonial troops fought under many different flags with various symbols and slogans -- rattlesnakes, pine trees, eagles, "Don't Tread on Me," "Liberty or Death," and "Conquer or Die," to name a few. The first flag had 13 stars on a blue field and 13 alternating red and white stripes for the 13 original colonies. Now there are 50 stars, one for each state in the Union, but the 13 stripes remain. Flag Day was first celebrated in 1877, on the flag's 100th birthday.

Do and Don'ts of the US Flag:
http://www.almanac.com/edpicks/flag.html