President Barack Obama laid out his vision for the next four years in a wide-ranging inaugural speech that called for political compromise, healthcare and immigration reform, equal social and economic rights, and agreement on fiscal policies.
The 44th US president told the American people to "seize" the moment as he took the oath of office at a public ceremony on the steps of the Capitol at the start of his second presidential term.
"This generation of Americans has been tested by crises that steeled our resolve and proved our resilience," said the President at the country's 57th inauguration since 1789.
"A decade of war is now ending," he said to the loudest cheer of his 18-minute, 2,095-word speech.
"An economic recovery has begun. America's possibilities are limitless, for we possess all the qualities that this world without boundaries demands: youth and drive, diversity and openness, an endless capacity for risk and a gift for re-invention.
"My fellow Americans, we are made for this moment, and we will seize it – so long as we seize it together."
He took the oath of office in a public ceremony a day after being sworn in for a second term, meeting a constitutional requirement that he take office by noon on January 20th. That date fell yesterday, pushing the public ceremony back to today.
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As his ceremonial re-inauguration fell on Martin Luther King Jnr Day, Mr Obama was sworn in on bibles owned by the civil rights leader and by US president Abraham Lincoln.
The president made his address before former presidents Bill Clinton and Jimmy Carter, US political leaders, and an estimated 700,000 supporters gathered on the National Mall running across the centre of Washington.
The number was less than the 1.8 million people who turned out for Obama's first inauguration in January 2009 after he made history by being elected the first black US president on promises of hope and change.
Today's attendance was still larger than the estimated 300,000 that saw the second inauguration of George W Bush in 2005.
Mr Obama's speech, which was slightly shorter and more pragmatic than his first inaugural address four years ago, made an historic first mention of gay rights in an inaugural address.
He touched on the policy battles facing him in his second four-year term, alluding to the upcoming fight with the Republican-led House of Representatives on raising the $16.4 trillion (€12.3 billion) debt ceiling to allow the US to pay its bills.
"For now decisions are upon us, and we cannot afford delay," he said.
"We cannot mistake absolutism for principle, or substitute spectacle for politics, or treat name-calling as reasoned debate. We must act, we must act knowing that our work will be imperfect. We must act, knowing that today's victories will be only partial."
Mr Obama called for social and economic equality, and spoke about better education and job creation as a means of recovery for the stalling US economy.
"Our country cannot succeed when a shrinking few do very well and a growing many barely make it," the President said. "We believe that America's prosperity must rest upon the broad shoulders of a rising middle class."
Mr Obama referred to the fight for equal rights for women, racial minorities, immigrants and gays, which is the first time gay rights has been mentioned in an inaugural address by a president.
"Our journey is not complete until our gay brothers and sisters are treated like anyone else under the law – for if we are truly created equal, then surely the love we commit to one another must be equal as well," said the President.
"Our journey is not complete until no citizen is forced to wait for hours to exercise their right to vote. Our journey is not complete until we find a better way to welcome the striving, hopeful immigrants who still see America as a land of opportunity."
The only reference to the debate on gun ownership in the aftermath of the school shooting in Newtown, Connecticut last month was the President's call for greater protection for children.
"Our journey is not complete until all our children, from the streets of Detroit to the hills of Appalachia to the quiet lanes of Newtown, know that they are cared for, and cherished, and always safe from harm," Mr Obama said.
On US foreign policy, the president reflected on the winding down of the wars in Iraq and Afghanistan and the need to move away from military action as a means of resolving international disputes.
"We, the people, still believe that enduring security and lasting peace do not require perpetual war," he said.
"America will remain the anchor of strong alliances in every corner of the globe; and we will renew those institutions that extend our capacity to manage crisis abroad, for no one has a greater stake in a peaceful world than its most powerful nation."
In a nod to the criticism of excessive government authority under his administration particularly during the last presidential election campaign, he praised enterprise and endeavour in the business world and in people's work.
"Through it all, we have never relinquished our skepticism of central authority, nor have we succumbed to the fiction that all society's ills can be cured through government alone," he said.
"Our celebration of initiative and enterprise; our insistence on hard work and personal responsibility, these are constants in our character."
The president's speech dealt broadly on the challenges facing him in the coming weeks while his State of the Union address on February 12th is expected to focus on specific policy targets.
Obama's address echoed the matter-of-fact speeches of Franklin D Roosevelt, the 32nd US president who had to tackle an economic depression and a world war in the 1930s and 1940s.
In a more forceful speech than his 2009 address, Obama said that Americans had an obligation to protect the environment, devoting one of the longest passages of his speech to the issue of climate change.
"We will respond to the threat of climate change, knowing that the failure to do so would betray our children and future generations," he said.
"Some may still deny the overwhelming judgment of science, but none can avoid the devastating impact of raging fires, and crippling drought, and more powerful storms. The path towards sustainable energy sources will be long and sometimes difficult.
"But America cannot resist this transition; we must lead it. We cannot cede to other nations the technology that will power new jobs and new industries – we must claim its promise"
Supporters made their way to the National Mall early as tight security forced the public to pass through heavily-manned security cordons and numerous metal detectors dotted around the city, though the public queues were far shorter than in 2009.
After his speech, Mr Obama attended the traditional inaugural lunch with US senators and congressmen when they dined on steamed lobster, hickory-grilled bison and apple pie.
Following the luncheon, the Obamas and the Bidens will make their way up Pennsylvania Avenue to the White House in a motorcade but are expected to walk part of the way, security concerns permitting.
This will be followed by a parade passing the Obamas in a viewing tower next to the White House. The parade will comprise bands and dancing troupes representing the 50 US states.
This evening the Obamas will dance before the camera and tens of thousands of attendees at two inaugural balls which are being held in the one venue this time around to avoid the transport chaos that brought Washington to a standstill four years ago.
