The presence of a "bill of rights", a list of exactly what rights are guaranteed to Americans by the Constitution, was a point of contention in the original debates. While both sides of the debate supported the protection of citizen's rights, one side worried that by enumerating particular rights, it would be assumed that citizens had no rights outside the particular ones enumerated. As a compromise, the delegates passed the Constitution, and agreed that they would later pass such as bill as a collection of amendments. Twelve such amendments were proposed; ten passed on December 15, 1791 to become what is now known as the Bill of Rights. One of the two amendments not passed was ratified over 200 years later to become Amendment Twenty-seven. The other, the original twelfth amendment, was never ratified. It is theoretically still pending, but unlikely to ever pass; it deals with setting the size of Congress, and proposes a formula that wouldn't work for today's population.
See also the general discussion at Constitution