US Republican presidential hopeful Mitt Romney has told students at a Christian university that marriage is between one man and one woman.
Mr Romney told the Liberty University commencement that marriage is an "enduring" institution that is reserved for one man and one woman.
He also said: "What you believe, how you live, what you value - it matters."
The crowd cheered his comments, made days after president Barack Obama embraced same-sex marriage.
Mr Romney avoided talking about his own Mormon faith, but said Judeo-Christian values have driven American success.
The Republican said that students at the university will bring "moral certainty" and "clear standards" to their jobs and lives.
He also said that America has trusted in "God, not man," since its founding.
Mr Romney was speaking in Lynchburg, Virginia.