Gay rights supporters celebrate after the US Supreme Court ruled that the US Constitution provides same-sex couples the right to marry, outside the Supreme Court building in Washington, June 26, 2015.[Photo/Agencies]

The Supreme Court case arose amid a transformation in American attitudes on gay rights and international change, including in Ireland last month, since the Netherlands became the first country to permit gay marriage nearly 15 years ago.

Advocates on both sides said on Friday the ruling will likely spawn a new round of litigation in areas such as parental rights and spousal benefits, as well as religion.

Declaring a right to marry does not revolve all rights for gay couples and their families. State laws vary regarding adoption, for example, and in some states where gay marriage was already allowed, lesbian parents have sued to get both of their names, not only the birth mother's, on the birth certificate.

Michigan, one of four states whose bans on gay marriage were challenged in Friday's case, earlier this month passed a law allowing private adoption agencies to refuse to place children with same-sex couples on religious grounds.

Separate lawsuits are already pending in lower courts over the timing of spousal benefits in the workplace and whether court rulings on marriage rights can be applied retroactively.

While Kennedy's opinion did not go beyond marriage rights for gays, it is likely to be tested in other situations. It represented the fourth time in nearly two decades that he has expansively interpreted the Constitution to protect gay rights. Once again, he laced his opinion with references to gay people's "dignity," concluding, "They ask for equal dignity in the eyes of the law. The Constitution grants them that right."

The question for future litigation is whether lower courts faced with other claims of discrimination will interpret the notion of equal dignity to apply beyond marriage.