Donald Trump is now the 47th president of the United States, as well as the 45th president, a businessman - and a man who knows how to put on a show.
Former presidents, Trump family members, tech royalty, and world politicians attended the historic event.
As the 78-year-old entered the Rotunda, where the inauguration ceremony was moved to due to freezing temperatures outside, he was met with cheers and applause.
He reached for his wife Melania, who he awkwardly tried to kiss, and greeted his predecessor, Joe Biden, who was standing opposite the Trump family with now-former Vice President Kamala Harris beside him.
During the inauguration ceremony, Mr Trump was pictured sitting next to Vice-President JD Vance, who also took the oath as his wife Usha stood next to him.
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Former US presidents in attendance included Bill Clinton with his wife, former presidential candidate and Trump rival Hillary Clinton.
Barack Obama was also there but without his wife Michelle, while George Bush attended with his wife Laura.
The newly-elected president gave his oath with his hand raised next to two bibles, one given to him by his mother and the other being the Lincoln Bible, first used in 1861 to swear in the 16th US president.
The Republican, whose first term in power lasted between 2017 and 2020, then gave a speech in which he announced some sweeping measures on migration, climate change and gender rights.
Mr Trump announced he will sign a "series of historic executive orders" and begin a "revolution of common sense".
He said he will declare a national emergency at the southern border while all illegal entry will "immediately be halted".
"Millions and millions of criminal aliens" would be returned and "the cartels" would be designated "as foreign terrorist organisations".
As expected, Mr Trump also reiterated he would rename the Gulf of Mexico as the Gulf of America - a remark which drew a chuckle from his former Democratic rival, Ms Clinton.
He also referenced an attempt on his life last year which saw him being shot in the ear during a rally in "a beautiful Pennsylvania field".
He said: "I was saved by God to make America great again."
The inauguration started at St John's Church, known as the Church of the Presidents, for one of the most private events of an inauguration, with no TV cameras allowed inside the small, yellow church.
After the intimate prayer service, incoming Vice President JD Vance went to meet outgoing VP Kamala Harris with their respective partners at the White House.
The Trumps headed to tea with the Bidens before the four of them were driven together to the swearing-in ceremony.
While the 46th and 47th presidents took tea, the Rotunda filled with guests and musicians, including Tesla and SpaceX CEO Elon Musk, who is Mr Trump's new government efficiency tsar, Amazon founder Jeff Bezos and Facebook and Meta co-founder and CEO Mark Zuckerberg.
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On the streets of Washington, thousands gathered to watch it live on screens.
On the eve of his inauguration, Mr Trump held a final rally in Washington DC, where he hinted at a blizzard of executive orders he would sign once he was back in the Oval Office.
He was joined on stage by Musk, where he later danced with members of the Village People, as they sang their hit YMCA.
After a candlelit dinner at the National Building Museum, Mr Trump headed back to Blair House, known as The President's Guest House, to prepare for one of the biggest days in the US political calendar.
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