In what could be one of the most important Supreme Court rulings in U.S. history, the high court will decide whether California's ban on gay marriage is constitutional.
Supporters of same-sex marriage see 41 reasons why the high court could uphold the ban.
While nine states allow same-sex partners to marry, or will soon, 41 states do not. Of those states, 31 have written gay marriage bans in their state constitutions.
"We were hoping that the Supreme Court would not take the case," said Thom Watson, who's engaged to marry his partner Jeff Tobacco.
"We could get married pretty soon but it just means more waiting," Tobacco said.
The court will decide California's Proposition 8 ban on gay marriage, as well as the Defense of Marriage Act, a federal law that denies tax breaks and health and pension benefits to legally married homosexuals.
Supporters of tradition marriage, like Randy Thomasson of Save California, are optimistic.
"But the US Supreme Court, I expect 4 or 5 justices to uphold Prop 8," he said.
Why? Because the U.S. Constitution doesn't address marriage, and the 10th Amendment says what is not in the federal powers belongs to the states."
But others fear a federal mandate for all 50 states.
"The ultimate question is whether the Supreme Court is ready to issue what you might call a Roe v Wade of same-sex marriage, to actually declare that it is unconstitutional for any state to limit marriage to unions of one man and one woman," the Family Research Council's Peter Sprigg said.
Meanwhile in Washington state, hundreds of homosexual couples lined up to collect marriage licenses after Gov. Christine Gregoire announced the passing of a voter-approved law legalizing gay marriage.
Many Christian leaders see this as a religious liberty issue.
"Whatever the Supreme Court says though the teaching is pretty clear, marriage is defined -- and that's what we're talking about, marriage -- is defined and it goes back scripturally to the very beginning of creation," Milwaukee Archbishop Jerome Listecki said.