It's a law stating that: 1(No state (or other political subdivision within the United States) need recognize a marriage between persons of the same sex, even if the marriage was concluded or recognized in another state. 2(The Federal Government may not recognize same-sex or polygamous marriages for any purpose, even if concluded or recognized by one of the states. <Source: http://en.wikipedia.org/wiki/Defense_of_Marriage_Act > And from what I can tell, it pretty much nullifies then entire concept of federally recognised gay marriage, and gives states the right to decide independantly whether they want to recognise gay marriage or not.

The Defense of Marriage Act, or DOMA, is a federal law, officially known as Pub. L. No. 104-199, 110 Stat. 2419 (Sept. 21, 1996) and codified at 1 U.S.C. 7 and 28 U.S.C. 1738C. The law has two effects.(2) 1) No state (or other political subdivision within the United States) need recognize a marriage between persons of the same sex, even if the marriage was concluded or recognized in another state. -- Unfortunately for the DOMA, the law is not on its side as the Warren Court benefited Gay Marriage with its opinion on Voting Rights. 2) The Federal Government may not recognize same-sex marriages for any purpose, even if concluded or recognized by one of the states. The DOMA relied on the States Rights Doctrine of the U.S. Constitution; however, the law is flawed since, in every case, a Right established by Congress and/or the U.S. Supreme Court has always conferred upon all states said Right. Hence, the DOMA is unconstitutional. Since the Warren verdict in 1967, Gay Marriage has been explicitly allowed by the U.S. Supreme Court invalidating the DOMA. -- One should note the DOMA was passed during an election year -- As a matter of law, a Gay Marriage Demand for Righthood should be filed in Federal Court relying on the Massachusetts decision and the U.S. Supreme Court decision. The U.S. Supreme Court could NOT refuse to hear the case, once it filters through the federal courts, due to Loving v. Virginia. It also could not refuse to state the DOMA is Unconstitutional and Gay Marriage is a right in all 50 states.