The case will be argued by the Indiana attorney general's office, who says the very challenge made by the gay couples is as an assault on marriage and the traditional family. They also claim striking down the same-sex prohibition could undermine the General Assembly's ability to prohibit other forms of marriage, such as polygamy.

Indiana's lawsuit is one of three pending challenges to state bans on same-sex marriages; similar suits have been filed in New Jersey and Massachusetts.

Evan Wolfson, executive director of the New York City-based Freedom to Marry Collaborative, said the issue in all three cases is basic civil rights.

"In the United States, we have experienced times when there were two water fountains, when there were two places to sit on the bus, when people of different races could not marry -- and people realized that was wrong," Wolfson said.

"Equality means equality, and if people believe marriage is good for non-gays, why would it not be good for gay people who love each other and their families?"

"Marriage is kind of the big enchilada in terms of the homosexual agenda. If same-sex couples are allowed all of the rights and benefits of marriage, that is the ultimate affirmation of their relationships," says Peter Sprigg, senior director of culture studies at the Family Research Council, an organization that lobbies against gay rights, and supports Indiana's ban on gay unions.