It resulted from lawsuits that challenged the voters' adoption of Proposition 8 on November 4, 2008, which amended the Constitution of California to outlaw same-sex marriage.

However, a revision, defined as a "substantial alteration of the entire constitution rather than to a less extensive change in one or more of its provisions,"[6] also requires the prior approval of 2/3 of each house of the California State Legislature.

California Attorney General Jerry Brown said that existing same-sex marriages would be unaffected, but other legal experts were uncertain.

[12] Plaintiffs in the three lawsuits included same-sex couples who had married or planned to marry, represented by the same legal team that argued and won In re Marriage Cases, Lambda Legal, the National Center for Lesbian Rights, and the ACLU of Northern California, as well as the cities of San Francisco and Los Angeles, and the county of Santa Clara.

Based on my duty to defend the law and the entire Constitution, I concluded the court should protect the right to marry even in the face of the 52 percent vote.

Other respondents include Mark B. Horton of the State Registrar of Vital Statistics and Linette Scott of the California Department of Public Health.

[24] The Campaign for California Families, a conservative religious organization,[25] also asked the court for permission to become an official party to all three cases.

[26] Represented by the Florida-based Liberty Counsel, the Campaign said in its motion to intervene that state officials would not adequately defend the rights of voters.

Kenneth Starr, dean of Pepperdine University School of Law and Whitewater controversy independent counsel, joined the Proposition 8 legal defence team that same day.

[29][30] Forty-four members of the California Legislature (about one-third of its membership) filed an amicus curiae brief in support of one of the three lawsuits.

The Anti-Defamation League, the Bar Association of San Francisco, and three other legal or civil rights groups also submitted letters supporting efforts to get the court to delay implementation of Proposition 8.

[27] Oral arguments took place on March 5, 2009, at the Supreme Court's headquarters in San Francisco, while thousands from both sides protested outside.

8 was a modest measure that left the rights of same-sex couples undisturbed under California's domestic-partner laws and other statutes banning discrimination based on sexual orientation," to the agreement of most of the judges.

"[35] Justice Moreno's dissent agreed with the petitioners' contention that "requiring discrimination against a minority group on the basis of a suspect classification strikes at the core of the promise of equality that underlies our California Constitution" and thus should be considered a revision.

[35] While oral arguments were ongoing within the court house in San Francisco, protests took place outside, with both sides sharing their views.

[38] On March 2, 2009, the California State Senate passed a resolution opposing Proposition 8, saying that "the initiative is a fundamental revision to the document, not an amendment, and therefore required deliberation by the Legislature and a two-thirds vote of both houses to put it on the ballot.

[40] On May 8, a "Meet in the Middle" march and rally took place in Fresno in an effort to sway Central California voters to support same-sex marriage, because they had "voted overwhelmingly for the ban".

[42] San Francisco City Attorney, Dennis Herrera, said that while it he was disappointed by the court's decision, it shows that the final round "could not be won in the legal arena".

[43] Proposition 8 supporters also planned to respond to the court ruling with public gatherings; Fresno pastor Jim Franklin, a leading opponent of same-sex marriage, opined that "if it were to go against the people, then there really should be rioting in the streets.