By Anthony Zurcher, BBC North America reporter
Analysis - If Donald Trump's speech at the Republican National Convention was billed as "midnight in America" - a pessimistic view of the current conditions in the US - then his message on inauguration day was that it's always darkest before the dawn. The nation was in peril, but America was about to be great again.
Donald Trump acknowledges the crowd during his swearing-in ceremony. Photo: AFP
Look back at RNZ's live coverage of the inauguration here.
Full text of the speech
In an address that was tonally consistent with Candidate Trump's campaign rhetoric, the president railed against a Washington elite that flourished while the American people suffered.
"While they celebrated in the nation's capital, there was little to celebrate for struggling families all across our land," he said.
He described a nation blighted with rusted-out factories, families "trapped in poverty", a public education system that deprived "young and beautiful" children of all knowledge and cities wracked by violent crime.
"This American carnage stops right here and stops right now," he said.
Early reports were that Mr Trump would offer a non-ideological appeal for national unity - and there were motions in that direction at times toward the end of his speech. This address, however, was very much aimed at his supporters - uniting the people with pitchforks against an out-of-touch establishment.
It was a call to arms for the disaffected Americans who fuelled the improbable rise of the New York real-estate mogul and reality television star to the White House.
He told them they would never again be forgotten or ignored. "Your voice, your hopes and your dreams will define our American destiny," he said.
This was not a message to the American people as a whole - many of whom likely feel the past resident of the White House, Barack Obama, reflected their beliefs and their diversity.
This was a speech for the angry, the frustrated, the American voters who turned out in places like Pennsylvania, Michigan, Florida and Ohio to shake their fist at the status quo and take a chance on a man who was unlike any presidential politician who came before him.
It should also serve as a wake-up call to American allies, as Mr Trump insisted that the US will put its own interests first both economically and militarily.
"We will follow two simple rules," he said. "Buy American and hire American."
For Mr Trump, giving this speech - and it clearly was a speech from his heart, if not directly from his pen - was the easy part. Making the promises to put America first, give power back to the people, bring jobs back, eradicate "radical Islamic terrorism" and rebuild US infrastructure isn't hard.
The challenge now will be to live up to his rhetoric as a different kind of president - and bring the rest of the nation along with him on the journey.
Congressional Republicans will advance their own priorities and follow their own path - one worn from years of tradition and ideology. What will Mr Trump do when their views diverge? Will an angry tweet or two suffice?
Democrats will dig into the trenches and plot how to undermine Mr Trump at every turn, counting the days until 2020.
American voters - at least ones in enough states to form an electoral college majority - have put their faith in Mr Trump. His presidency will be a remarkable experiment for American democracy, as it's clear after this speech that Mr Trump intends to govern as he campaigned.
The new president has set the stage. Now, as he said on the steps of the Capitol, it is the hour of action.
He has four years to make his supporters proud and prove all the doubters wrong.
- BBC