Crowds are thronging the US Capitol to watch Barack Obama be publicly sworn in for his second term as US president.
Four years and one day after President Obama first took his first oath of office, America is once again celebrating his Inauguration. This time the schedule includes performances by Beyonce and Katy Perry, a parade with more than 2,000 members of the military and two Inaugural balls.
Mr Obama will take the oath of office before hundreds of thousands of spectators on Washington's National Mall.
Festivities include black-tie balls, a parade, and musical performances.
Mr Obama was formally sworn in at a small White House ceremony on Sunday - the US Constitution dictates presidential terms begin on 20 January.
In the famous Blue Room with his wife and daughters, the Democratic president rested his hand on a Bible that was used for many years by Michelle Obama's family, and was sworn in by Chief Justice John Roberts.
According to the words prescribed by the US Constitution, Mr Obama swore he would "faithfully execute the office of president of the United States, and will to the best of my ability, preserve, protect and defend the Constitution of the United States".
He will repeat those words at Monday's public inauguration, placing his left hand on Bibles owned by legendary American civil rights leader Martin Luther King Jr and President Abraham Lincoln.
Then, Mr Obama will give an inaugural address in which he will lay out his vision for a second term.
Mr Obama is not expected to preview his policy agenda on Monday - he will address that in next month's State of the Union speech, when he will ask bitterly divided lawmakers to come together and reduce gun violence, overhaul the immigration system and reduce the yawning federal budget deficit.
Speaking at a reception for supporters late on Sunday, Mr Obama suggested he would dwell on the "common good" and the "goodness, the resilience, neighbourliness, the patriotism" of Americans.
"What we are celebrating is not the election or the swearing-in of the president," Mr Obama said. "What we are doing is celebrating each other and celebrating this incredible nation that we call home."
By Monday afternoon, Mr Obama will have taken the oath four times - as many as President Franklin D Roosevelt.
Four years ago, Mr Obama repeated the oath privately to make sure all constitutional obligations were met after Justice Roberts tripped over the words in the public ceremony.
Following Monday's ceremony, Mr Obama will have the traditional lunch with US lawmakers in the capitol building's Statuary Hall.
Later, the president is expected to walk at least part of the parade route down Pennsylvania Avenue toward the White House.Vice-President Joe Biden, who was also sworn in on Sunday - by Supreme Court Justice Sonia Sotomayor - will repeat his oath publicly as well.
In the evening, the Obamas will don formal evening attire for several lavish inaugural balls in Washington.The zone surrounding the National Mall in the US capital is in virtual lockdown, with movement of people and vehicles tightly restricted.
White tents, trailers and generators are set up along the parade route, while nearby buildings have been adorned with red, white and blue bunting.
Officials estimate about 700,000 people will attend the inauguration, down significantly from 2009, when about 1.8 million people witnessed Mr Obama be sworn in as America's first black president.
"We wanted to see history, I think, and also for the children to witness that anything is possible through hard work," David Richardson of Atlanta, in the crowd with his two young children, told the Associated Press.