Two of the key plaintiffs are Paul Katami and Jeff Zarrillo, a Burbank, California, couple who want to marry but can't because of Proposition 8.

CNN: SHARE THIS

"This is about our freedom and our liberty, " Katami said.

CNN: Day Two of same-sex marriage at Supreme Court

The California couples, Kris Perry and Sandy Stier of Berkeley and Paul Katami and Jeff Zarrillo of Burbank, filed their federal lawsuit in May 2009 to overturn the same-sex marriage ban that voters approved the previous November.

NPR: Calif. Gay Marriage Argument At High Court Tuesday