What is Constitution Day?
Most Americans know that July 4th is our nation's birthday. Far fewer Americans know that September 17th is the birthday of our government, the date in 1787 on which delegates to the Philadelphia Convention completed and signed the U.S. Constitution.
The ideas on which America was founded--commitments to the rule of law, limited government and the ideals of liberty, equality and justice--are embodied in the Constitution, the oldest written constitution of any nation on Earth. Constitution Day is intended to celebrate not only the birthday of our government, but the ideas that make us Americans.
From National Constitution Center, http://www.constitutionday.us/, retrieved 9.16.14
The National Constitution Center is the first and only institution in America established by Congress to "disseminate information about the United States Constitution on a non-partisan basis in order to increase the awareness and understanding of the Constitution among the American people."