Under Article V of the Constitution, there are two ways to propose amendments to the Constitution and two ways to be ratified by the states. To propose amendments, two-thirds of both houses of Congress can vote to propose an amendment, or two-thirds of the state legislatures can ask Congress to call a national convention to propose amendments. To ratify amendments, three-fourths of the state legislatures must approve them, or ratifying conventions in three-fourths of the states must approve them.

The Supreme Court has said that ratification must be within "some reasonable time after the proposal." Beginning with the 18th amendment, Congress traditionally set a definite period for ratification. In the case of the 18th, 20th, 21st, and 22nd amendments, the period set was seven years, but there has been no determination as to just how long a "reasonable time" might extend.