Constitution Day (or Citizenship Day) recognizes the ratification of the United States Constitution and those who have become U.S. citizens. It is observed on September 17, the day the U.S. Constitutional Convention signed the Constitution in 1787.
You can learn more at the National Endowment for the Humanities’ Constitution Day site.
Stephen Wasby, Constitution Day 2013
Text of the Constitution
(from the National Archives Web site)