After a heady night of celebration Donald Trump will start working to unite the nation he vowed to put first and deliver on his campaign promises.
The 45th President of the United States capped off an historic day with appearances at three balls across Washington DC, where he thanked his supporters and told them: “We are not playing games. The work begins.”
However away from the jubilation in the ballrooms there were ugly scenes as thousands of anti-Trump protesters took to the streets in the American capital and across the US to vent their anger.
And Mr Trump’s first full day in office is expected to see 200,000 people join a women’s march in Washington, with similar events planned in cities around the world.
The new president did not wait long to set his plans in motion, with his first executive order aimed at one of his predecessor’s signature healthcare policies.
Barack Obama had barely left Washington when Mr Trump took his place in the Oval Office to sign off the order seeking the “prompt repeal” of Obamacare.
And just yards away there was another symbol of a change - a bust of Sir Winston Churchill removed during the Obama years had been returned.
From the White House Mr Trump appeared at the first of the evening’s celebratory events, the Liberty Ball, with his wife Melania, now First Lady, at his side.
“You’re going to see things happen over the next few weeks,” he told the crowds.
“We want to see great things happen for our great country. We want to make America great again and we will.”
The President’s ambition was even evident in the choice of song for the first dance with the First Lady - Frank Sinatra’s My Way.
The famous Twitter fan was soon to take over Mr Obama’s @POTUS handle, a stern-looking President Trump looking on.
At the second ball of the evening the crowd roared with apparent approval when he asked whether he should “keep the Twitter going”.
“It’s a way of bypassing dishonest media,” he quipped.
As the social media takeover was completed policies from the new administration appeared on the White House website.
Confirming the fears of many environmentalists, Mr Trump underlined his intentions on climate change, saying he is “committed to eliminating harmful and unnecessary policies such as the Climate Action Plan and the Waters of the US rule”.
He also said the US would be “committed to a foreign policy focused on American interests and American national security”, vowing to pursue “joint and coalition military operations” to defeat so-called Islamic State and other radical Islamic terror groups.
On the steps of the Capitol Building earlier on Friday the president promised to put “America first” as he set out a nationalist agenda.
The address broke with tradition as he sought to hammer home populist political points against globalisation and the Washington elite.
Promising to “rebuild our country and restore its promise for all of our people”, he said: “From this day forward it is going to be only America first, America first.”
Around 1.8 million people turned out for President Barack Obama’s first inauguration in 2009, but photographs of the National Mall suggest considerably fewer travelled to Washington DC to see his successor sworn in at the Capitol building on Friday.
Meanwhile thousands joined protests in the city, with chaotic scenes outside the Washington Post building where demonstrators torched a limousine.
Elsewhere windows were damaged by people carrying metal poles and hammers, and police had to use hand-held water cannon, smoke grenades and tear gas to disperse the troublemakers, with at least 217 arrested, while six officers suffered minor injuries.
Other protests took place around the world as Mr Trump took the oath of office on the steps of the Capitol building just before noon local time, his family and the outgoing president looking on.
Imploring the US to come together, Mr Trump said that a united America “is totally unstoppable”.
All decisions on trade, taxes, immigration and on foreign affairs will be made to “benefit American workers and American families” he pledged.
He added: “America will start winning again, winning like never before.”
Prime Minister Theresa May congratulated Mr Trump on taking office, and said that in previous conversations he was committed to strengthening the “special relationship” between Britain and the US.