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.

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

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

One of the plaintiff couples -- Paul Katami and Jeff Zarrillo of Burbank, California, who want to marry but can't because of Proposition 8 -- contend the state is discriminating against them because of their sexuality.

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

The Supreme Court hearing is the moment Perry and Stier, along with Paul Katami and Jeff Zarrillo of Burbank, have been waiting for since they agreed four years ago to be the named plaintiffs and public faces of a well-funded, high-profile effort to challenge Proposition 8 in the courts.

NPR: AP Interview: Couple Reflects On Gay Marriage