Under Article Five, the Constitution can be amended in two ways: through a two-thirds majority vote in Congress or by a two-thirds vote of a national convention at the request of at least two-thirds of the states. To become operative, three-quarters of the states, or state ratifying conventions, must ratify.
There have been 33 amendment proposals sent to the states for ratification since the establishment of the Constitution, all via Congress. Twenty-seven amendments have been made to the Constitution, including the Bill of Rights, the first 10 amendments. State legislatures have at various times used their power to pressure Congress into proposing an amendment, but many legal questions remain how the amendment process would work via this route.
To become operative, an amendment, whether proposed by Congress or a national Constitutional Convention, must be ratified by either the legislatures of three-quarters of the states or state ratifying conventions in three-quarters of the states. Congress has specified the state legislature ratification method for all but one amendment.
Since the turn of the 20th century, amendment proposals sent to the states for ratification have generally contained a seven-year ratification deadline. An amendment with an attached deadline that is not ratified by the required number of states within the set time period is considered inoperative and rendered moot.
An amendment becomes operative as soon as it reaches the three-quarters of the states threshold, and once certified by the Archivist of the United States, it officially becomes an article of the Constitution.