Joe Biden will be sworn in as the 46th president of the United States, during a day steeped in tradition and ceremony that nonetheless has been altered due to the pandemic and tight security after the January 6 attack on the Capitol.
So what happens next? Here's what you need to know ...
Night at Blair House
Joe Biden and his wife Jill spent last night in the lavish Blair House, located opposite the White House on Lafayette Square, which the US government uses to host special guests and visiting dignitaries.
This morning, Mr Biden, a devout Catholic, will attend mass at St Matthew's cathedral in Washington, and has invited Congressional leaders from both political parties.
Senator Mitch McConnell and Congressman Kevin McCarthy will represent the Republicans, while Democratic Senator Chuck Schumer and Congresswoman Nancy Pelosi will also attend, sources have told AFP.
Taking the oath
Mr Biden will then travel in a motorcade to the Capitol, the site of the 6 January riot by supporters of outgoing President Donald Trump, where the inauguration ceremony gets under way at 11am (4pm Irish time).
He will be sworn in after Vice President-elect Kamala Harris takes her vow, then will give his inaugural speech, during which he is expected to outline his vision to tackle America's multiple crises and his plan to "build back better".
The National Mall that runs from the Capitol to the Lincoln Memorial will be closed due to Covid-19 fears and because of tight security stemming from the 6 January attack.
Lady Gaga is due to sing the national anthem, while Jennifer Lopez is also set to give a musical performance. Garth Brooks will also perform at the ceremony.
As is custom, the newly inaugurated 46th US president will then dine with members of Congress in the Capitol building.
Arlington National Cemetery
In the afternoon, the new US President will head to Arlington National Cemetery just outside Washington to place a wreath on the Tomb of the Unknown Soldier.
Mr Biden will be accompanied by former presidents Barack Obama, George W Bush and Bill Clinton. Donald Trump, who is shunning the day's events, will not be there.
From Arlington, Joe Biden will travel by motorcade to the White House and is expected make the last part of the journey on foot and enter his new home surrounded by a military cordon.
He is due to sign his first executive orders shortly after arriving.
Honouring the pandemic's victims
At 8.25pm, Mr Biden and Ms Harris will give a speech at the Lincoln Memorial, honouring the 400,000 people who have died from Covid-19 in America.
Shortly after, actor Tom Hanks will host a show called "Celebrating America" that will be broadcast on all major US networks.
Jon Bon Jovi, the Foo Fighters, John Legend, Demi Lovato, Bruce Springsteen, Justin Timberlake and Luis Fonsi are among the guests expected to perform.
There will be special coverage of the US Presidential Inauguration on RTÉ One at 3.30pm today