If everything is proceeding as scheduled, oral arguments should be getting started inside the courtroom.
[Updated at 10:11 a.m. ET]
The atmosphere probably pretty somber inside the court, but outside the speakers are blaring with music and the occasional chant: "Gay, straight, black, white - marriage is a civil right!"
CNN contributors David Frum and LZ Granderson have both taken to the mic, keeping the crowd charged up.
"No agency of the government can do for anyone what loving spouses do for each other," Frum said. "Today your families gather before this house of law to claim the right to live as others do without fear."
"I did not come here to ask anybody permission to love. I did not come here to (seek ) approval," said Granderson. "... I am here because 14 times the Supreme Court (ruled that marriage is) a fundamental right, and gay and lesbian couples deserve their fundamental rights!"
"Same-sex couples are not here asking for a seat at the table because we've always been here," he added. "We're not here at the steps of Supreme Court to beg. ... I too sing, America."
[Updated at 10 a.m. ET]
Nope, we don't have cameras in the courtroom, but the high court should be in session at this point. After a few minutes of routine business, oral arguments should get underway at about 10:15 a.m. In addition to Jeffrey Toobin, CNN has Correspondent Joe Johns and Supreme Court producer Bill Mears watching the arguments firsthand. Stay tuned here for developments.
[Updated at 9:50 a.m. ET]
As the justices gather, the court of public opinion is already weighing in - certainly on Twitter. At 9:30 a.m. ET, five of the top U.S. trends were related to the hearing today. Though, this being Twitter, #ThoughtsInBed was also riding high.
[Updated at 9:43 a.m. ET]
Today's arguments have sparked conversation beyond the steps of the Supreme Court. Supporters and opponents of same-sex marriage are capturing the moment on social media. Here's one from NOH8 Campaign, who support marriage equality:
"Today #Prop8 has its day in front of the Supreme Court. RT if you agree it's time for #MarriageEquality! #NOH8"
Opponents of same-sex marriage have also shown up in droves in Washington, but the rallies have kept peaceful.
[Updated at 9:26 a.m. ET]
Less than an hour away from the start of oral arguments and protests outside the Supreme Court are gaining momentum. Supporters of same-sex marriage and LGBT rights are holding a rally, celebrating the historic significance of today's events.
"We are all participants of American history today - let's get this party started!" two of the organizers shouted at a cheering audience.
The crowd is holding signs, saying, "Married with pride" and "Marriage is love, commitment and family."
"Condemn hatred, embrace marriage!" the crowd chanted.
Among the speakers is retired Lt. Col. Linda Campbell, a 25-year military veteran, who was allowed to bury her partner, Nancy Lynchild, at Willamette National Cemetery. It is believed to be the first case of its kind, the same-sex spouse of a member of the military to be buried in a national cemetery.
"I know the spirit of my spouse Nancy is smiling on us today," Campbell said today.
[Updated at 8:34 a.m. ET]
Looks like Justice Kennedy will definitely be the one to watch today.
"What am I looking to? Justice Kennedy in his questioning," said California Lt. Gov. Gavin Newsom who, as San Francisco mayor in 2004, stoked controversy by ordering City Hall to issue marriage licenses to same-sex couples.