There are two ways an amendment can be proposed.
1. The proposed Amendment must pass with two-thirds majority vote in both the House of Representatives and U.S. Senate or
2. A Constitutional Convention can be called by two-thirds of the state legislatures. None of the 27 Amendments to the U.S. Constitution have been proposed this way.
If the amendment passes both the House and the Senate with two-thirds majority, it then goes to the states. Three-fourths of the states, or 38, must ratify the amendment. Currently 38 states have laws with prohibit same-sex marriage or Defense of Marriage Acts.
The most recent amendment to the Constitution was ratified in 1992. The 27th Amendment prevents Congress from passing a law to give itself a raise before the next election.
The Equal Rights Amendment, which would have set into law, equality between men and women, passed both the Senate and the House, but failed in the states.
Most proposals to amend the Constitution fail.
