To ratify an amendment to the U.S. Constitution, the legislatures in three-fourths of the states or ratifying conventions in three-fourths of the states must approve the proposed amendment. If two-thirds of Congress votes in favor of an amendment, it passes to the states for ratification.
Article V of the Constitution specifies the procedures for proposing and ratifying amendments. Ratification must take place within a reasonable time after the proposal of an amendment, and Congress typically specifies a period of ratification. Most amendments to the Constitution have been ratified after three-fourths of the state legislatures approved them. The 21st Amendment, which repealed Prohibition, was the only ratification passed by approval by ratifying conventions.