Thirty-three amendments to the United States Constitution have been proposed by the United States Congress and sent to the states for ratification since the Constitution was put into operation on March 4, 1789. Twenty-seven of these, having been ratified by the requisite number of states, are part of the Constitution. The first ten amendments were adopted and ratified simultaneously and are known collectively as the Bill of Rights. Six amendments adopted by Congress and sent to the states have not been ratified by the required number of states. Four of these amendments are still technically open and pending, one is closed and has failed by its own terms, and one is closed and has failed by the terms of the resolution proposing it.