US President Barack Obama has delivered his inaugural address launching a second term in the White House with a call for national unity.
Mr Obama, 51, repeated the oath of office before a cheering crowd of hundreds of thousands at the Capitol building in Washington on Monday.
He was formally sworn in at the White House on Sunday but repeated the oath - led by Supreme Court Chief Justice John Roberts - at the public inauguration.
The 44th president of the United States laid his hands on two Bibles; one that belonged to president Abraham Lincoln and another to civil rights leader Martin Luther King.
As he stepped onto the podium at the Capitol building before the oath, the crowd chanted "Obama, Obama" and waved US flags.
In his address, Mr Obama urged Americans to reject political absolutism and partisan rancour.
"We cannot mistake absolutism for principle, or substitute spectacle for politics, or treat name-calling as reasoned debate," he said.
The president said the United States must make hard choices to reduce cost of health care and the size of its deficit.
"But we reject the belief that America must choose between caring for the generation that built this country and investing in the generation that will build its future," he said.
Mr Obama said America's prosperity must rest upon the broad shoulders of a rising middle class.
"We must harness new ideas and technology to remake our government, revamp our tax code, reform our schools, and empower our citizens with the skills they need to work hard or learn more, reach higher.
"But while the means will change, our purpose endures. A nation that rewards the effort and determination of every single American; that is what this moment requires."
Outlining his ambitions for a second term, the president said he would support democracy from "Asia to Africa, from the Americas to the Middle East".
He vowed the US would respond to the threat of climate change, "knowing that the failure to do so would betray our children and future generations."
Mr Obama said the people's guiding star remains that all are created equal.
"For our journey is not complete until our wives, our mothers, and daughters can earn a living equal to their efforts.
"Our journey is not complete until our gay brothers and sisters are treated like anyone else under the law," he said, and that all children know that they are cared for.
The president's private swearing in on Sunday was necessary to fulfil the constitutional mandate that every presidential term begin at noon on 20 January.
Dating back to 1821, if the date fell on a Sunday, public celebrations have been postponed to another day.