One case concerns the constitutionality of a voter referendum banning homosexual marriage in California; the other concerns the constitutionality of a federal law that excludes same-sex couples from receiving government benefits.
Same-sex couples are getting marriage licenses in Washington state, where voters approved gay marriage in November.
Major events in the U.S. gay rights movement
June, 1969: Gays in New York City riot to protest police raids of the Stonewall Inn, a bar in Greenwich Village. Event is considered the birth of the gay rights movement in America.
December, 1973: The American Psychiatric Association removes homosexuality from its list of mental illnesses.
November, 1978: America’s first openly-gay elected official, San Francisco Board of Supervisors member Harvey Milk, is assassinated.
December, 1993: The Pentagon implements “Don’t Ask, Don’t Tell”, a policy that allows gay military service as long as a member’s homosexuality remains secret.
September, 1996: President Bill Clinton signs the Defense of Marriage Act, which bars federal recognition of same-sex marriage and stipulates that no state must honor a same-sex marriage performed in another state.
June, 2003: The U.S. Supreme Court rules anti-sodomy laws are unconstitutional.
May, 2004: Massachusetts becomes the first state to legalize same-sex marriage.
November, 2008: California voters approve Proposition 8, which strips gay couples of marriage rights in the state.
December, 2010: President Barack Obama signs the repeal of "Don’t Ask, Don’t Tell".
May, 2012: President Obama announces his personal support for same-sex marriage.
November, 2012: Maryland, Maine, and Washington become the first states to affirm same-sex marriage by popular vote.
December, 2012: The U.S. Supreme Court announces it will hear appeals of lower court rulings striking down both the Defense of Marriage Act and California’s Proposition 8.
"I look forward to the day when the federal government will recognize the marriages of all Americans. And I am hoping that will happen during my lifetime," she said.
Last week, the U.S. Supreme Court agreed to hear the case after lower courts declared the federal Defense of Marriage Act unconstitutional. Critics of the law include Democratic U.S. Senator Dianne Feinstein.
“Same-sex couples live their lives like all marriage couples. They share financial expenses; they raise children together; they care for each other in good times and in bad," she said.
Congressionally-appointed attorneys will defend the law before the Supreme Court, and are endorsed by Republican Representative Steve King.
“All of human experience points to one committed relationship between a man and a woman as the core building block to society," he said.
The Justice Department stopped defending the law under President Barack Obama, who made headlines earlier this year.
“I think same-sex couples should be able to get married," he said.
The Supreme Court will also consider a California voter referendum that stripped same-sex couples of marriage rights in 2008. Lower courts ruled Proposition 8 unconstitutional.
The high court could hear oral arguments in both cases as early as March and rule on both cases in June. Possible outcomes range from the high court affirming no constitutional right to same-sex marriage and upholding the Defense of Marriage Act to striking down the law and legalizing homosexual marriage nationwide.
Pro-gay rights Mayor Jeffrey Prang said, “There are lots of good things that could come out of this decision, and lots of really bad things could come out of this decision.”
Anti-gay rights activists predict Proposition 8 will be upheld. “The Constitution of the United States does not have marriage in it. And the 10th Amendment [to the Constitution] says what is not in the federal powers belongs to the states," said Randy Thomasson of savecalifornia.com.
Public opinion surveys show that a slight majority of Americans favor same-sex marriage rights. Changing views will not be lost on the Supreme Court, according to legal analyst Elizabeth Wydra.
“The justices are human beings, so they are not completely immune to public opinion," she said. "I think the real question for them is going to be, 'Do they want to be on the wrong side of history?'”
One of America’s most-contentious social issues will have its day in court, in the highest court in the land.