The court’s 4-to-3 decision, striking down two state laws that had limited marriages to unions between a man and a woman, will make California only the second state, after Massachusetts, to allow same-sex marriages. The decision, which becomes effective in 30 days, is certain to be an issue in the presidential campaign.

“In view of the substance and significance of the fundamental constitutional right to form a family relationship,” Chief Justice Ronald M. George wrote of marriage for the majority, “the California Constitution properly must be interpreted to guarantee this basic civil right to all Californians, whether gay or heterosexual, and to same-sex couples as well as to opposite-sex couples….