Signed into effect by former U.S. president Bill Clinton in 1996, the federal law known as the Defense of Marriage Act (DOMA) defines marriage as the union of a man and a woman. In addition, it gives certain powers to the states, allowing each state’s government to determine its own laws regarding marriage.

Written by Georgia State Representative Bob Barr, the Defense of Marriage Act was originally intended to expand states’ rights, by overriding previous laws that required states to recognize marriages performed outside their borders. The reason for this arose in 1993, when Hawaii became the first state to recognize same-sex marriages. Lawmakers in many other states were concerned about how Hawaii’s ruling would affect their state’s laws, as many were vehemently opposed to same-sex marriages and did not feel the state should be required to recognize such unions. The the Defense of Marriage Act was developed in reaction.

After passing through the United States’ House of Representatives with a vote of 342-67, DOMA was brought before the Senate, and passed with a vote of 85 to 14. Several states enacted constitutional amendments to define marriage in the same terms as the federal government, granting marriages solely to heterosexual couples. In addition, under the Defense of Marriage Act, these same states were no longer required to recognize same-sex marriages performed in states where such unions were allowed.

Although several states passed laws to recognize same-sex marriages, under the terms of the Defense of Marriage Act, only marriages between a man and a woman are recognized by the federal government. In other words, even if a state recognizes the marriage, the federal government does not — meaning partners in a same-sex marriage do not receive the same rights that heterosexual couples receive. For example, same-sex couples are not eligible for spousal Social Security or veterans’ benefits, and they do not qualify for the same tax credits that are available to heterosexual couples. Immigration privileges, inheritance protection, parental rights, and health insurance benefits are also affected by the act.

Many critics of DOMA have attempted to repeal the act, citing the Due Process and Equal Protection Clauses of the 14th Amendment as grounds for its reversal. In 2009, numerous suits were filed against the federal government to challenge the constitutionality of the act. None of these attempts were successful, however, and the Defense of Marriage Act has remained in effect. As of June 2010, only five of the 50 U.S. states grant same-sex marriage licenses, and of the remaining states, only three recognize such unions.