There are two paths that proposed amendments can take to become law. The first path is this: An amendment is proposed in Congress; two-thirds of both houses must then approve it (if they do not, then the proposal ends here); if approved in both houses of the U.S. Congress, the proposed amendment is sent to the legislatures (or conventions) of each state of the union; three-fourths of all the state legislatures must then approve it (by whatever rules each state legislature uses); once three-fourths of the states approve it, the amendment is made (if three-fourths of the states do not approve it, the amendment fails to become law).

The second path is this: The legislatures of two-thirds of the states ask for an amendment to be made to the U.S. Constitution; Congress then calls a convention to propose it; then the proposed amendment becomes a law when it is ratified by the legislatures in three-fourths of the states. While this path has never been taken, it’s an important provision nonetheless since it allows for a popular, state-based proposal to be considered.