List of defense of marriage amendments to U.S. state constitutions by type

There are several different types of what have been unofficially termed defense of marriage amendments in the United States. These amendments to U.S. state constitutions have been enacted in order to prevent civil unions or same-sex marriages from being legalized, though some of the amendments bar only the latter. As of 2008, Massachusetts and California are the only U.S. states to allow same-sex marriage.

Twenty-seven defense of marriage amendments have been adopted. Of these, eight make only same-sex marriage unconstitutional, seventeen make both same-sex marriage and civil unions unconstitutional, and two are unique. Hawaii's amendment is unique in that it does not make same-sex marriage unconstitutional; rather, it allows the state to limit marriage to opposite-sex couples. Virginia's amendment is also unique; it prevents the state from recognizing private contracts that "approximate" marriage. Observers have pointed out that such language encompasses private contracts and medical directives.

This list only covers bans of civil unions, private contracts between same-sex couples and same-sex marriage in state constitutions; mere laws are not listed. The text of these amendments sometimes runs several paragraphs. In this event, excerpts of the most important phrases or sentences are included in this list.

State constitutional amendments are typically approved first by the legislature or special constitutional convention and then by the voters in a referendum.N- In some states, one or both of these steps is repeated.N- The percentages shown in the list are results from the referendum stage, not the legislative stage.