The U.S. Constitution has 27 amendments. The first 10, constituting the Bill of Rights, were written in 1791 as part of the original document. As of 2014, the most recent amendment to the Constitution was the 27th Amendment, added to the Constitution in 1992, which regulated congressional pay rates.
In order to amend the Constitution, the amendment must be proposed by both houses of Congress. A proposal is achieved by passing the amendment with a two-thirds majority vote. Following the proposal, three-fourths of the state's legislatures must also approve the amendment by a two-thirds vote. As of 1919, there is a seven-year time limit on proposal and ratification.