(CNN) -- President Joe Biden's inauguration on Wednesday looked a bit different from past ceremonies ushering in a new administration.
There is, after all, immensely heightened security in Washington, DC, and a swirling pandemic, not to mention the absence of the outgoing president, the first time that's happened in more than a century and a half.
It's been a day rife with history and packed with unforgettable moments. Here's a look at some of the highlights so far:
Trump leaves the White House
Though former President Donald Trump did not attend Biden's swearing-in ceremony, he was publicly seen several times, including when he left the White House as president for the last time shortly after 8 a.m. ET.
Before boarding Marine One with the former first lady, Trump told reporters at the White House it was a "great honor" to serve as 45th President of the United States before saying goodbye.
Trump speaks at Joint Base Andrews before heading to Florida
Trump also held a final farewell ceremony, where both he and former first lady Melania Trump delivered remarks.
The former President thanked his family and chief of staff, and promised to "always fight." He also wished the incoming Biden administration "great luck," though he didn't mention his successor by name.
Melania Trump, meanwhile, told attendees that "being your first lady was my greatest honor." The two then boarded Air Force One for the last time just before 9 a.m., taking the presidential plane to their Florida home.
Biden attends church
Just after the Trumps boarded Air Force One, Biden and first lady Jill Biden headed over to Cathedral of St. Matthew the Apostle in DC, where they attended mass with their family, Vice President Kamala Harris and her family. They were joined by the congressional leaders of both parties.
Incoming presidents typically attend services on the morning of their inauguration, often at St. John's Episcopal Church, a small church across Lafayette Square from the White House known as "The Church of the Presidents."
Biden arrives at Capitol
Biden arrived at the US Capitol shortly after 11 a.m. and Harris and her husband, Doug Emhoff, accompanied him and Jill Biden up the steps of the iconic building.
When Biden arrived at the inauguration stage, he greeted his predecessor and former boss, former President Barack Obama, on his way to his seat. He received a lengthy ovation from those gathered on the stage and sat down at 11:19 a.m.
Harris and Obama first bump
As she walked to her seat on the inaugural stage, Harris shared double fist bumps with Obama.
The gesture, exchanged shortly before Harris was sworn in as vice president, carried symbolic weight as Obama and Harris made history as the first African Americans to serve as president and vice president, respectively.
Harris similarly fist bumped Michelle Obama, who made history as the country's first African American first lady.
Harris is sworn in as vice president
Harris took the oath of office at 11:42 a.m. She used two Bibles during the oath, which was administered by Supreme Court Justice Sonia Sotomayor.
Harris officially became the first female, first Black and first South Asian vice president at noon.
Biden is sworn in as the 46th president
After being sworn in, Biden delivered an inaugural address in which he called for unity and pledged to be a "president for all Americans," including those who did not support his campaign at his inauguration address.
The President also offered a forewarning his remarks, describing the nation as weathering a "winter of peril" amid the coronavirus pandemic.
Singers and poet perform
The inauguration also featured several celebrity performances, including a rendition of the National Anthem by Lady Gaga. Jennifer Lopez sang a medley of American musical selections including "This Land is your Land" and "America the Beautiful," and Garth Brooks performed "Amazing Grace."
Amanda Gorman, the nation's first-ever youth poet laureate, also delivered a poem in which she challenged Americans to "leave behind a country better than the one we were left" and unify.
Pence and Harris share a laugh
Former Vice President Mike Pence, who attended the ceremony even though Trump did not, was met with bipartisan applause when he and his wife, Karen Pence, walked out onto the inaugural stands earlier Wednesday.
Later, as Harris and Emhoff bid the Pences farewell outside the Capitol, the two couples shared a laugh as the Pences began their private life.
Biden signs first presidential documents
Biden signed three documents after the ceremony outside the Capitol finished, including an Inauguration Day Proclamation, nominations to Cabinet positions and nominations to sub-Cabinet positions.
Biden and Harris receive congressional gifts
The President and vice president also received congressional gifts, as is customary, including a painting by a Black painter from the Civil War presented to Biden by Sen. Roy Blunt, a Missouri Republican. Minnesota Democratic Sen. Amy Klobuchar presented Biden and Harris with Lenox crystal vases, while House Speaker Nancy Pelosi and now-Senate Minority Leader Mitch McConnell presented the President and vice president with American flags.
Biden and Harris attend wreath-laying at Arlington
Biden and Harris went from the Capitol to Arlington National Cemetery for a wreath-laying ceremony with three former presidents -- Obama, George W. Bush and Bill Clinton -- at the Tomb of the Unknown Soldier.
Biden walks in inaugural parade
Biden and his family got out of the presidential motorcade to walk down the stretch of Pennsylvania Avenue outside the White House. The President stopped a few times to greet people along the route, including Washington Mayor Muriel Bowser and NBC's Al Roker.
The Bidens enter the White House
Shortly before 4 p.m., Biden entered the White House for the first time as the 46th commander in chief. He and the first lady paused for a moment on the North Portico as "Hail to the Chief" played.
They embraced, waved to cameras and walked alongside their extended family into the Grand Foyer to begin his presidency.
Harris swears in new Democratic senators
Harris returned to the Capitol to swear in three new Democratic senators: Georgia's Jon Ossoff and Raphael Warnock, and California's Alex Padilla, who replaced Harris in the chamber.
Their swearing-in officially gave Democrats control of the Senate for the first time since they lost the chamber in 2014. Harris will wield power as the Senate's crucial tie-breaking vote.
Biden takes aim at Trump's legacy with early executive actions
Biden got down to work in the White House later Wednesday, finalizing over a dozen executive moves by signing a flurry of executive orders, memorandums and directives to agencies.
"There's no time to start like today," Biden told reporters in the Oval Office as he began signing a stack of orders and memoranda. "I'm going to start by keeping the promises I made to the American people."
This story has been updated with additional developments Wednesday.
™ & © 2021 Cable News Network, Inc., a WarnerMedia Company. All rights reserved.