The U.S. Supreme Court has agreed to hear two challenges to state and federal laws dealing with the recognition of gay and lesbian couples to legally wed.

Oral arguments will likely be held in March, with a ruling expected by late June.

One appeal to be heard involves the federal Defense of Marriage Act (DOMA), which denies federal benefits to same-sex couples legally married in their own state. The second is a challenge to California's Proposition 8, a voter-approved referendum that took away the right of same-sex marriage that previously had been approved by state courts.

Currently, Maryland, Washington, Maine, Massachusetts, Connecticut, Iowa, Vermont, New Hampshire, New York and the District of Columbia issue marriage licenses to same-sex couples. Minnesota voters also rejected an effort to ban such unions through a constitutional amendment.

Five states - Delaware, Hawaii, Illinois, New Jersey and Rhode Island - currently allow civil unions that provide rights similar to marriage.

Here is a timeline showing the progression of same-sex marriage across the country.

Timeline:

– September 21, 1996 – President Clinton signs the Defense of Marriage Act banning federal recognition of same-sex marriage and defining marriage as "only a legal union between one man and one woman as husband and wife."

– December 20, 1999 – The Vermont Supreme Court rules that gay and lesbian couples should be given the same rights as heterosexual couples.

– November 18, 2003 – The Massachusetts Supreme Court rules that a ban on same-sex marriage is unconstitutional.

– February 20, 2004 – Sandoval County, New Mexico, begins issuing same-sex marriage licenses, but they are nullified by the state attorney general that same day.

– February 12 – March 11, 2004 – Nearly 4,000 same-sex couples get marriage licenses in San Francisco.

– February 24, 2004 – President Bush announces support for a federal constitutional amendment banning same-sex marriage.

– February 27, 2004 – New Paltz, New York, Mayor Jason West performs same-sex marriages for about a dozen couples.

– March 3, 2004 – In Portland, Oregon, the Multnomah County Clerk's office issues marriage licenses for same-sex couples. Benton County follows, on March 24.

– June 7, 2004 – The Supreme Court of Ulster County, New York, issues a permanent injunction to stop Jason West, the mayor of New Paltz, New York, from marrying same-sex couples.

– March 11, 2004 – The California Supreme Court orders San Francisco to stop issuing marriage licenses to same-sex couples.

– May 17, 2004 – The first legal same-sex marriages in U.S. history are performed in Cambridge, Massachusetts.

– July 14, 2004 -A proposed constitutional amendment to ban same-sex marriage fails in the U.S. Senate. A procedural vote to move the measure to the Senate floor for final consideration fails 48-50 - 12 votes shy of the 60 required by Senate rules.

– August 12, 2004 –  The California Supreme Court orders San Francisco officials, including Mayor Gavin Newsom, not to license additional same-sex marriages, pending resolution of the constitutional challenges to state marriage statutes.

– September 30, 2004 – The U.S. House of Representatives votes against amending the Constitution to prohibit gay marriage.

– October 5, 2004 – A Louisiana judge throws out an amendment to the state constitution banning gay marriage, because the ban also includes civil unions.

– November 2, 2004 – Eleven states pass constitutional amendments defining marriage as being between a man and a woman only: Arkansas, Georgia, Kentucky, Michigan, Mississippi, Montana, North Dakota, Ohio, Oklahoma, Oregon and Utah.

– March 14, 2005 – A Superior Court judge rules that California's law that limits marriage to a union between a man and a woman is unconstitutional.

– April 14, 2005 – Oregon's Supreme Court nullifies the same-sex marriage licenses issued there in 2004.

– May 12, 2005 –  A federal judge strikes down Nebraska's ban on protection and recognition of same-sex couples.

– August 5, 2004 – A Washington judge rules the state's law defining marriage is unconstitutional.

– January 18, 2005 – The Louisiana State Supreme Court reinstates the constitutional amendment banning gay marriage that was thrown out in October 2004.

– September 6, 2005 – The California Legislature passes a bill to legalize same-sex marriage. The legislature is the first in the U.S. to act to sanction gay marriages without being forced by a court order.

– September 14, 2005 – The Massachusetts Legislature rejects a proposed amendment to its state constitution to ban same-sex marriages.

– September 29, 2005 – California Gov. Arnold Schwarzenegger vetoes the bill legalizing same-sex marriage.

– October 1, 2005 – A Connecticut law goes into effect that allows civil unions, and an amendment is included that defines marriage as the union of a man and a woman.

– October 7, 2005 – The Massachusetts Supreme Judicial Court hears a case challenging a 1913 law prohibiting nonresidents from marrying in Massachusetts if the marriage is prohibited in their home state. The law has been used in recent years to prevent same-sex couples from getting married.

– November 8, 2005 – Texas becomes the 19th state to adopt a constitutional amendment banning gay marriage.

– January 20, 2006 – A Maryland judge rules the state's law defining marriage is unconstitutional.

– March 30, 2006 – The highest court in Massachusetts rules that same-sex couples who live in other states cannot get married in Massachusetts unless gay marriage is legal in their home states.

– May 16, 2006 – Georgia's constitutional ban on same-sex marriage is struck down in Fulton County Superior Court. The court says a measure approved by voters in 2004 violated a rule that limits ballot questions to a single subject. Appeals are pending.

– June 6, 2006 – Alabama voters pass a constitutional amendment to ban same-sex marriage.

– July 6, 2006 – The New York Court of Appeals rules that a state law banning same-sex marriage is legal, and the Georgia Supreme Court upholds the state's constitutional amendment banning same-sex marriage.

– November 7, 2006 – Constitutional amendments to ban same-sex marriage are on the ballot in eight states.  Seven states pass theirs - Colorado, Idaho, South Carolina, South Dakota, Tennessee, Virginia, and Wisconsin - while Arizona voters reject the ban.

– December 21, 2006 – Civil unions are legalized in New Jersey. The law goes into effect on February 19, 2007.

– January 1, 2008 – The civil unions law signed by New Hampshire Gov. John Lynch in April 2007 goes into effect.

– May 15, 2008 –  The California Supreme Court rules that the state's ban on same-sex marriages is unconstitutional. The decision goes into effect on June 16.

– October 10, 2008 – The Connecticut Supreme Court rules that the state must allow gay and lesbian couples to marry.

– November 4, 2008 – Voters in California approve Proposition 8, which will amend the state's constitution to ban same-sex marriage. Voters in Arizona and Florida approve similar amendments to their state constitutions.

– March 23, 2009 – The Vermont state Senate votes 26 to 4 to legalize same- sex marriages. The bill goes before the state's House of Representatives on March 27, 2009.  Vermont Gov. Jim Douglas says he will veto a same-sex marriage bill if it comes across his desk.

– April 3, 2009 – The Iowa Supreme Court strikes down a state law banning same-sex marriage.

– April 7, 2009 – Vermont becomes the fourth state to legalize same-sex marriages after both the state Senate and House of Representatives overturn a veto by Gov. Jim Douglas. The Senate vote is 23-5, while the House vote is 100-49.

– April 27, 2009 – Same-sex marriage becomes legal in Iowa as the court ruling comes into effect. Dozens of couples across the state apply for marriage licenses and at least three marriages are performed.

– May 6, 2009 – Same-sex marriage becomes legal in Maine, as Gov. John Baldacci signs a bill less than an hour after the state legislature approves it.

– May 6, 2009 – New Hampshire lawmakers pass a bill legalizing same-sex marriage. The House passes the bill in a 178-167 vote after the Senate approved the legislation in a 13-11 vote.

– May 26, 2009 – The California Supreme Court upholds the passage of Proposition 8, banning same-sex marriage. However, 18,000 such marriages performed before Proposition 8 will remain valid.

– May 31, 2009 – Nevada legalizes domestic partnerships. The state Assembly votes 28-14 to override Gov. Jim Gibbons' veto.

– June 17, 2009 – President Barack Obama signs a memorandum granting some benefits to same-sex partners of federal employees.

– July 7, 2009 – A new District of Columbia law recognizing same-sex marriages performed elsewhere takes effect.

– November 3, 2009 – Voters in Maine repeal the state's law allowing same-sex marriage.

– December 15, 2009 – The Washington, D.C., City Council votes to legalize gay marriage, 11-2.

– January 1, 2010 – Same-sex marriage becomes legal in New Hampshire.

– March 3, 2010 – Same-sex marriage becomes legal in Washington, D.C.

– July 9, 2010 – Judge Joseph Tauro of Massachusetts rules that the 1996 Defense of Marriage Act is unconstitutional because it interferes with a state's right to define marriage.

– July 15, 2010 – A federal appeals court upholds the District of Columbia law, rejecting an anti-same-sex marriage referendum.

– August 4, 2010 – Chief U.S. District Judge Vaughn Walker of the United States District Court for the Northern District Of California decides in Perry v. Schwarzenegger that Prop 8 is unconstitutional.

– January 31, 2011 – Illinois Gov. Pat Quinn signs the Illinois Religious Freedom Protection and Civil Union Act. It will go into effect June 1, 2011.

– February 1, 2011 – The Iowa House of Representatives passes Joint Resolution 6, an amendment proposal banning same-sex marriage, by a vote of 62-37.

– February 16, 2011 – Hawaii's Senate passes a measure to legalize same-sex unions. Gov. Neil Abercrombie says that he will sign the bill, which will take effect January 1, 2012.

– February 23, 2011 – The Obama administration instructs the Justice Department to stop defending the constitutionality of the Defense of Marriage Act in court.

– April 25, 2011 – King & Spalding, the private law firm hired by House Speaker John Boehner, backs out of defending the Defense of Marriage Act.

– May 12, 2011 – Delaware Gov. Jack Markell signs legislation allowing civil unions between same-sex couples in the state. The bill will take effect January 1, 2012.

– June 14, 2011 –  Gov. Andrew Cuomo of New York proposes the Marriage Equality Act, a bill to legalize marriage for same-sex couples.

– June 14, 2011 – The U.S. District Court for the Northern District of California upholds a lower court ruling that invalidated Proposition 8's ban on same-sex marriage as unconstitutional. The ruling had been challenged when the lower court's judge was found to be gay.

– June 24, 2011 – The New York Senate votes to legalize same-sex marriage. Gov. Andrew Cuomo signs the bill just before midnight, and the bill goes into effect July 24, 2011.

– July 2, 2011 – Rhode Island Gov. Lincoln Chafee signs legislation making that state the fifth to allow civil unions between same-sex couples.

– September 30, 2011 – The Pentagon issues new guidelines allowing military chaplains to perform same-sex ceremonies.

– January 1, 2012 – Civil unions become legal in Delaware and Hawaii.

– January 30, 2012 – Legislation to legalize same-sex marriage in the state of Washington passes a House committee vote and heads to the Senate. Gov. Chris Gregoire is in favor of the bill.

– February 1, 2012 – The Washington state Senate passes a bill to legalize same-sex marriage, by a vote of 28-21. On February 8, 2012, the House approves the measure by a vote of 55-43.

– February 7, 2012 – A three-judge panel with the 9th U.S. Circuit Court of Appeals in San Francisco rules that Proposition 8, the voter-approved same-sex marriage ban, violates the Constitution.

– February 13, 2012 – Same-sex marriage is signed into law in Washington state by Gov. Christine Gregoire.  The law will go into effect in June unless opponents halt its implementation by putting it on the November 2012 ballot.

– February 13, 2012 – The New Jersey state Senate passes a bill to legalize same-sex marriage by a vote of 24-16.

– February 17, 2012 – New Jersey Gov. Chris Christie vetoes a bill legalizing same-sex marriage. New Jersey lawmakers have until the legislative session ends in January 2014 to override Christie's veto and would need a two-thirds majority in both houses to succeed.

– February 23, 2012 – The Maryland Senate passes a bill to legalize same-sex marriage. The bill passed the Maryland House vote earlier in the month, and Gov. Martin O'Malley has promised to sign it into law. The law will go into effect in the summer if it survives a likely court challenge.

– May 8, 2012 – North Carolina voters pass a constitutional amendment banning same-sex marriage, putting a ban that already existed in state law into the state's charter.

– May 9, 2012 – Excerpts from an interview with ABC air in which President Barack Obama endorses same-sex marriage, the first such statement by a sitting president.  He feels that the legal decision should be up to the states.

– May 30, 2012 – A lawsuit is filed in Illinois by nine same-sex couples, challenging the constitutionality of a state law that denies same-sex couples the right to marry.

– May 31, 2012 – The 1st U.S. Circuit Court of Appeals in Boston rules that the Defense of Marriage Act discriminates against gay couples.

– June 5, 2012 – The 9th Circuit U.S. Court of Appeals in San Francisco denies a request to review an earlier court decision stating that California’s Proposition 8 violates the Constitution. A stay on same-sex marriages in California remains in place until the issue is exhausted in the courts.

– October 18, 2012 – The 2nd U.S. Circuit Court of Appeals rules that the Defense of Marriage Act violates the Constitution's equal protection clause, deciding in favor of widow Edith Windsor, an 83-year-old lesbian who sued the federal government for charging her more than $363,000 in estate taxes after being denied the benefit of spousal deductions.

–  November 6, 2012 – Voters in Maryland, Washington and Maine passed referendums legalizing same-sex marriage. This is the first time same-sex marriage has been approved by a popular vote in the United States. Voters in Minnesota rejected a ban on the practice.

–  December 5, 2012 – Washington Gov. Christine Gregoire, signs Referendum 74, the Marriage Equality Act, into law.

–  December 7, 2012 – The U.S. Supreme Court announces it will hear two constitutional challenges to state and federal laws dealing with the recognition of gay and lesbian couples to legally wed. Oral arguments in the appeal will likely be held in March, with a ruling by late June.

Civil Unions and Domestic Partnerships:

Civil unions grant couples most of the rights of state civil marriages, but provide none of the federal benefits of marriage, such as Social Security benefits. These rights include spousal support, medical decision-making privileges, access to a partner's insurance, and hospital visitation rights. Many cities and counties across the nation offer domestic partner registries that are open to gay couples or unmarried heterosexual couples.

Legal Recognition of Same-Sex Marriage by State:

Marriage  

• Maryland
• Washington
• Maine
• Massachusetts
• Connecticut
• Iowa
• Vermont
• New Hampshire
• New York
• Washington, D.C.

Civil Union or Domestic Partnership

• Delaware (Civil Union)
• Hawaii (Civil Union)
• Illinois (Civil Union)
• New Jersey (Civil Union)
• Rhode Island (Civil Union)
• California (Domestic Partnership)
• Oregon (Domestic Partnership)
• Nevada (Domestic Partnership)

Limited Domestic Partnership, Reciprocal Beneficiary, Designated Beneficiary

• Colorado (Designated Beneficiary)
• Hawaii (Reciprocal Beneficiaries)
• Maine (Limited Domestic Partnership)
• Wisconsin (Limited Domestic Partnership)

Domestic Partnership Health Care Benefits for State Employees  

• Massachusetts
• New Hampshire
• Hawaii
• Illinois
• New Jersey
• New Mexico
• New York
• Oregon
• Rhode Island
• Vermont
• Washington
• Washington, D.C.
• California
• Connecticut
• Iowa
• Maine
• Montana
• Alaska
• Arizona

Legal Recognition of Same-Sex Marriage Outside the U.S.:

• Argentina – 2010
• Belgium – 2003
• Brazil – 2011
• Canada – 2005
• Iceland – 2010
• Mexico City – 2009
• Netherlands – 2001
• Norway – 2008
• Portugal – 2010
• South Africa – 2006
• Spain – 2005
• Sweden – 2009