The court's session ends on June 29, and it is widely speculated that the nine justices will wait until that day to issue a ruling on one of the most divisive issues in the country. But rulings are also being delivered Thursday and Friday, and the court doesn't say in advance which rulings are coming out on which days, heightening the suspense.
The plaintiffs and stakeholders have been eagerly awaiting the historic decision since the hearing in April. They have been preparing for the outcome, one way or the other.
"We are anxious and excited for hopefully a positive decision from the court. It will certainly be a huge disappointment for so many who have worked so hard for this moment if the court rules against fairness and equality for all Americans," Janson Wu, executive director of the Gay and Lesbian Advocates and Defenders, said in an interview.
The case, known as Obergefell vs. Hodges, involves four combined cases from Kentucky, Ohio, Michigan and Tennessee. The key questions to rule on are whether the U.S. Constitution requires states to give marriage licences to same-sex couples and whether the constitution requires states to recognize a marriage between two people of the same sex that was performed legally in another state.
Couples can now marry in 36 states and the District of Columbia. Depending on how the court decides, that number will either shrink or expand to all 50 states. Some states have same-sex marriage because of ballot initiatives or changes to their own state constitutions. A Supreme Court ruling against same-sex marriage wouldn't affect those states.
Justices' comments scrutinized
Other states currently allow same-sex marriage because their bans were quashed in lower court rulings. If the Supreme Court rules against same-sex marriage, then the legal status of couples in those states could become confusing and uncertain.
After April's hearing, the justices' comments and questions to the lawyers were scrutinized for clues to which way they might be leaning.
"I thought the hearing went well for us. I think the other side realizes that too," said Brian Brown, president of the National Organization for Marriage, which is against same-sex marriage.
Despite some confidence that his side will win, Brown said his group has been busy since April preparing a Plan B in case they lose. That includes sending letters last week to all declared Republican presidential candidates asking them to commit to taking specific steps to preserve the traditional definition of marriage should they be elected.
Those actions include working to overturn any Supreme Court decision that changes the definition and appointing justices and an attorney general that would uphold the one man and one woman definition of marriage. They also include trying to amend the U.S. Constitution so it stipulates that marriage can only be between opposite-sex couples.
Loss would be 'illegitimate'
"If we were to lose, it will be an illegitimate decision on the part of the Supreme Court," Brown said, adding, "we will do everything in our power to rally the millions of Americans "who support marriage between a man and a woman only."
Both sides are looking to Justice Anthony Kennedy as the swing vote. Kennedy said during the hearing that the definition of marriage has "been with us for millennia," and he seemed to question whether it is the court's place to "know better" and change it.
That comment is what is giving those against same-sex marriage optimism, but at the same time, Kennedy has shown sympathy in the past to gay rights causes, and during the hearing he talked about the dignity of same-sex couples.
"The Conservatives made much of this false notion that marriage has always been and always should be this one definition, which is utterly untrue," said Wu. "I think Kennedy, hopefully, will see how inaccurate that description is."
Kelly Noe, one of the plaintiffs in the Kentucky case, and her wife are fighting to have both of their names kept on their daughter's birth certificate. They have been trying to carry on with normal life while they await a potentially life-changing ruling.
Noe said in an interview that she thinks the hearing went well for their side, but she knows the court can be unpredictable.
"My gut feeling is that they will say no on question one and yes on question two," said Noe. "I really don't think they're going to say no on both. I will be very surprised if that's the case."
Noe said it would be "heartbreaking" if they lost, but if they do, they won't give up.
"We will continue this fight until our marriage is recognized."