In recent years, the debate over same-sex marriage has grown from an issue that occasionally arose in a few states to a nationwide controversy. Indeed, in the last five years, the debate over gay marriage has been heard in the halls of the U.S. Congress, at the White House, in dozens of state legislatures and courtrooms, and in the rhetoric of election campaigns at both the national and state levels. Moreover, the battle over whether gays and lesbians should be allowed to wed shows no signs of abating. In the last year alone, three states have banned same-sex marriage and four states have legalized the practice.

Recently, both sides in the debate have scored important victories. In April 2009, for example, Iowa’s Supreme Court ruled that the state’s constitution guarantees gays and lesbians the right to wed; the high court in Connecticut had issued a similar ruling in May 2008. Meanwhile, gay marriage advocates also won important legislative victories in a number of states, beginning in April 2009 when the Vermont Legislature legalized same-sex marriage. The Vermont law marked the first time gay marriage was legalized as the result of a statute rather than a court ruling. By the end of May 2009, two other state legislatures, those in Maine and New Hampshire, followed suit, bringing the total number of states that allow same-sex marriage to six. Finally, in June 2009, President Barack Obama granted family medical leave and certain other benefits to the same-sex partners of federal workers. (The presidential memorandum did not include health insurance coverage, which would require congressional approval.)

Opponents of gay marriage also have had some success in recent years. In November 2008, for instance, voters in California, Florida and Arizona approved ballot initiatives amending their state constitutions to prohibit same-sex marriage, raising the total number of states that have passed such constitutional amendments to 29. (Arizona voters had previously rejected a constitutional ban in November 2006.) The vote in California, on a ballot measure known as Proposition 8, was particularly notable since it overturned a May 2008 California Supreme Court ruling legalizing same-sex marriage in that state. Passage of Proposition 8 also prompted an entirely new court battle over whether the just-approved ballot initiative itself was constitutional. That battle ended in May 2009, when the California Supreme Court upheld the constitutionality of Proposition 8. (See The Constitutional Dimensions of the Same-Sex Marriage Debate.)

Differing Views

Most supporters of same-sex marriage contend that gay and lesbian couples should be treated no differently than their heterosexual counterparts and that they should be able to marry like anyone else. Beyond wanting to uphold the legal principles of nondiscrimination and equal treatment, supporters say there are very practical reasons behind the fight for marriage equity. They point out, for instance, that homosexual couples who have been together for years often find themselves without the basic rights and privileges that are currently enjoyed by heterosexual couples who legally marry – from the sharing of health and pension benefits to hospital visitation rights.

Most social conservatives and others who oppose same-sex marriage argue that marriage between a man and a woman is the bedrock of a healthy society because it leads to stable families and, ultimately, to children who grow up to be productive adults. Allowing gay and lesbian couples to wed, they contend, will radically redefine marriage and further weaken it at a time when the institution is already in serious trouble due to high divorce rates and a significant number of out-of-wedlock births. Moreover, many predict that giving gay couples the right to marry will ultimately lead to granting people in polygamous and other nontraditional relationships the right to marry as well.

The American religious community is deeply divided over the issue of same-sex marriage. The Catholic Church and many evangelical Christian groups have played a leading role in public opposition to gay marriage, while mainline Protestant churches and other religious groups wrestle with whether to ordain gay clergy and perform same-sex wedding ceremonies. Indeed, the ordination and marriage of gay persons has been a growing wedge between the socially liberal and conservative wings of the Episcopal, Lutheran and Presbyterian churches, leading some conservative congregations and even whole dioceses to break away from their national churches. (See Religious Groups’ Official Positions on Same-Sex Marriage.)

[For more recent public opinion data on same-sex marriage, see Most Say Homosexuality Should Be Accepted By Society.]

The same-sex marriage debate is not solely an American phenomenon. Many countries, especially those in Europe, have grappled with the issue as well. Since 2001, seven nations – the Netherlands, Belgium, Spain, Canada, South Africa, Sweden and Norway – have legalized gay marriage. (See Gay Marriage Around the World.)

The Beginning of the Debate

Gay Americans have been calling for the right to marry, or at least to create more formalized relationships, since the 1960s, but same-sex marriage has only emerged as a national issue within the last 20 years. The spark that started the debate occurred in Hawaii in 1993, when the Hawaii Supreme Court ruled that an existing law banning same-sex marriage would be unconstitutional unless the state government could show that it had a compelling reason for discriminating against gay and lesbian couples.

Even though this decision did not immediately lead to the legalization of gay marriage in that state (the case was sent back to a lower court for further consideration), it did spark a nationwide backlash. Over the next decade, legislatures in more than 40 states passed what are generally known as Defense of Marriage Acts (DOMAs), which define marriage solely as a union between a man and a woman. While a few of these laws have been struck down, 36 states still have DOMAs on the books. In addition, in 1996 the U.S. Congress passed, and President Bill Clinton signed, a federal DOMA statute that, for purposes of federal law, defines marriage as a union between a man and a woman. The statute also asserts that no state can be forced to legally recognize a same-sex marriage performed in another state. The enactment of a federal DOMA is significant since the federal protections and benefits conferred by marriage are stipulated in over 1,000 laws and policies, including Social Security, family medical leave and federal taxation and immigration policies.

In the late 1990s, Alaska, Nebraska and Nevada amended their state constitutions to prohibit same-sex marriage. These constitutional changes were aimed at taking the issue out of the hands of judges. Conservatives, in particular, feared that without constitutional language specifically defining marriage, many judges would take it upon themselves to interpret other constitutional provisions broadly so as to allow a right to same-sex marriage.

Amid widespread efforts in many states to prevent same-sex marriage, there was at least one notable victory for gay-rights advocates during this period. In 1999, the Vermont Supreme Court ruled that gay and lesbian couples were entitled to all the rights and protections associated with marriage. However, the court left it up to the Vermont Legislature to determine how to grant these rights to same-sex couples. The following year, the legislature approved a bill granting gay and lesbian couples the right to form civil unions, which grant most of the legal rights of marriage but not the title.

The Massachusetts Decision and Its Aftermath

For a while, the debate over gay marriage seemed to fade from the public eye. But the issue was suddenly catapulted back into the headlines in November 2003, when the highest state court in Massachusetts ruled that the state’s constitution guaranteed gay and lesbian couples the right to marry. Unlike the Vermont high court’s decision four years earlier, the ruling in this case, Goodridge v. Massachusetts Department of Public Health, left the Massachusetts Legislature no option for how to implement the court’s decision: the court required the legislature to pass a law granting full marriage rights to same-sex couples. (See The Constitutional Dimensions of the Same-Sex Marriage Debate.)

In the days and weeks following the 2003 Massachusetts decision, some cities and localities – including San Francisco; Portland, Ore.; and New Paltz, N.Y. – began issuing marriage licenses to gay couples. Television images of long lines of same-sex couples waiting for marriage licenses outside government offices led some social conservatives and others to predict that same-sex unions would soon be a reality in many parts of the country. But these predictions proved premature.

To begin with, the marriage licenses issued to gay couples outside Massachusetts were later nullified, since none of the mayors and other local officials involved had the authority to grant marriage licenses to same-sex couples. More significantly, the Massachusetts decision led to another major backlash at the federal and state levels. In the U.S. Congress, conservative lawmakers, with support from President George W. Bush, attempted to pass an amendment to the U.S. Constitution that would have banned same-sex marriage nationwide. However, efforts to obtain the two-thirds majority needed in both houses to pass the amendment fell short in 2004 and again in 2006.

Recent State Actions

Opponents of gay marriage have had better luck at the state level, especially in recent years. Prior to 2004, only four states had approved constitutional amendments either banning same-sex marriage or, in the case of Hawaii, taking the issue away from the state’s courts. In 2004, however, voters in 13 states passed referenda amending their constitutions to prohibit same-sex marriage. Thirteen additional states took the same step between 2005 and 2008, bringing the total number of states with gay marriage bans in their constitutions to 29. (See Graphic: State Policies on Same-Sex Marriage.)

Most of the states that have approved constitutional amendments banning gay marriage are in the more socially conservative South and Midwest, although, as noted, voters in a more socially liberal state, California, narrowly approved a ban in 2008. On the East Coast, however, all but one state in New England (Rhode Island) allows same-sex marriage. Between the coasts, only one state, Iowa, has so far recognized gay marriage. In other states, including more socially liberal jurisdictions such as New York, Washington state and Maryland, high courts have rejected the argument that gay marriage is a constitutional right.

Civil Unions and Domestic Partnerships

While battles have been raging in many states over whether to accept or ban same-sex marriage, a number of states have enacted laws that establish civil unions or domestic partnerships, both of which aim to give gay and lesbian couples many or most of the rights and responsibilities of matrimony without actually granting them the right to wed. Civil unions were first created in Vermont in response to a 1999 ruling by the Vermont Supreme Court ordering the state legislature to provide same-sex couples “the common benefits and protections that flow from marriage under Vermont law.” (Vermont has since enacted a same-sex marriage law that supersedes its civil union statute.) Currently, only one state, New Jersey, allows for civil unions.

California and Oregon have nearly identical provisions that allow both heterosexual and homosexual couples to register as domestic partners and claim all state benefits conferred on husbands and wives. California’s law was enacted in 1999 and was extended to include all marital benefits in 2005. During a brief period of time, from June 16 to Nov. 4, 2008, California allowed same-sex couples to wed, but gay and lesbian couples who did not marry during this brief period may once again register under the state’s domestic partnership statute. Oregon’s law was enacted in 2007. Washington has a domestic partnership law – adopted in 2007 and expanded in 2008 – that includes most, but not all marital benefits. Nevada recently enacted a broad domestic partnership law that will take effect in October 2009. Hawaii has a narrower domestic partner registry, put in place in 1997, that conveys only a handful of benefits, including hospital visitation rights and inheritance without a will.

Finally, a number of states that have not approved same-sex marriage, including New York and Rhode Island, now recognize gay nuptials legally performed elsewhere, as does the District of Columbia.

The Road Ahead

Gay marriage advocates hope that their recent victories in Iowa and Vermont will give their cause momentum in other states. And indeed, other state legislatures – in New Jersey and New York – have recently considered measures that would make gay marriage legal.

Opponents of same-sex marriage note that whenever voters have had an opportunity to weigh in on the issue – even in a more socially liberal state such as California – they almost always vote against gay marriage. These opponents hope to continue placing constitutional bans on the ballot and are targeting Iowa, among other states, in the hope of reversing that state’s recent Supreme Court decision.

Both sides also are gearing up for a renewed fight at the federal level. For example, there has been some movement in the U.S. Congress to amend or repeal the 1996 Defense of Marriage Act, a step President Obama supports. Indeed, in June 2009, when Obama granted limited benefits to the same-sex partners of federal workers, he stated that he could not offer them medical insurance because of the federal DOMA and took the opportunity to call for its repeal. While it is difficult to predict where the next battle will be fought and what the outcome will be, it is safe to assume that the gay marriage debate will remain part of the nation’s legal and political landscape for years to come.

This report was written by David Masci, Senior Research Fellow, Pew Research Center’s Forum on Religion & Public Life.

Photo credit: Martin Ruetschi/Keystone/Corbis