By Jan. 1, same-sex couples will have the right to marry in nine states and the District of Columbia, and President Obama has said he backs that right.
Previous Supreme Court cases provide few hints as to how the court will rule. Although Justice Anthony Kennedy, who may cast the deciding vote, backed gay rights in 1996 and 2003 rulings, neither case involved marriage.
California voters approved Proposition 8, banning gay marriages, in 2008. The ballot initiative reversed a decision by the California Supreme Court, which five months earlier had said the state constitution guaranteed the right to gay marriage.
In challenging the law, Olson joined forces with David Boies, his opponent from Bush v. Gore, the Supreme Court case that resolved the 2000 presidential election deadlock. The pair set out to win a Supreme Court ruling establishing same-sex marriage as a constitutional right.
At the appeals court level, they instead won a narrower ruling with limited applicability beyond California's borders. The San Francisco-based 9th U.S. Circuit Court of Appeals said Proposition 8 violated the constitutional guarantee of equal protection by stripping same-sex couples of a right they once had — and that heterosexual couples would continue to possess.
Writing for the majority on the 2-1 court, Judge Stephen Reinhardt said the measure "serves no purpose, and has no effect, other than to lessen the status and human dignity of gays and lesbians in California, and to reclassify their relationships and families as inferior to those of opposite-sex couples."
Supporters of Proposition 8, led by former state Sen. Dennis Hollingsworth, appealed to the Supreme Court. They argued that the lower court's reasoning was a "suggestion that any experiment with the definition of marriage is irrevocable."
The group also contended in court papers that Proposition 8 "furthers society's interest in responsible procreation and child-rearing."