State conventions are assemblies of delegates convened to ratify proposed constitutional amendments or, historically, the Constitution itself. Article V establishes two methods for ratifying amendments: approval by three-fourths of state legislatures (the method used for 26 of 27 amendments) or approval by conventions in three-fourths of the states.
Congress chooses which ratification method to use when proposing an amendment. The convention method has been used only once—for the 21st Amendment in 1933, which repealed Prohibition. Supporters chose conventions instead of legislatures because they believed state lawmakers, many elected before Prohibition became unpopular, would not reflect current public sentiment.
All 50 states held ratifying conventions, and 38 approved the amendment within 10 months. State conventions also played a crucial role in the Constitution's original adoption: the Constitutional Convention in Philadelphia sent the proposed Constitution to state ratifying conventions rather than state legislatures, and nine states' approval brought it into effect in 1788. Delaware ratified first, and New Hampshire became the decisive ninth state. This convention method avoided the requirement under the Articles of Confederation for unanimous state legislative approval.