In the wake of the violent and deadly breach of the U.S. Capitol by a pro-Trump mob and the ongoing coronavirus pandemic, the inauguration of President-elect Joe Biden and Vice President-elect Kamala Harris will be unlike any other in American history.

Here's what to know and how to watch.

-ABC News' Kennedey Bell

Trump has left a note in the Oval Office for Biden, ABC News has learned.

The content of the note is not clear at this time.

The development comes after Biden's communications director told ABC's "Good Morning America" that Trump still hadn't made direct contact with the president-elect.

-ABC News' Johnathan Karl and John Santucci

Biden, a devout Catholic and the second to take the presidency, is starting Inauguration Day with Mass at the Cathedral of St. Matthew the Apostle in Washington, joined by the top congressional leaders.

House Speaker Nancy Pelosi -- another devout Catholic -- outgoing Senate Majority Leader Mitch McConnell, Senate Minority Leader Chuck Schumer and House Minority Leader Kevin McCarthy joined Biden for the service, along with his wife, Jill Biden, Vice President-elect Kamala Harris and her husband Doug Emhoff -- the nation's first second gentlemen -- Biden extended invitations to top congressional leaders. In a show of unity, all accepted those invites.

Joint Congressional Committee on Inaugural Ceremonies Chairs Sen. Amy Klobuchar, D-Minn., and House Majority Leader Steny Hoyer, D-Md., were also in attendance.

Faith has played a significant role in Biden's life -- when he lost his wife Neilia and young daughter Naomi in a horrific 1972 car accident in which his young sons Beau and Hunter were severely injured. Beau died of a brain tumor in 2015 at age 46.

An Irish violinist will play and soprano Renee Fleming will sing "On Eagle's Wings" - the Catholic hymn Biden said his son loved and which he quoted from in his November victory speech.

With the trappings of a Trump rally on a cold and windy morning, President Trump arrived at Joint Base Andrews in Maryland just after 8:30 a.m. on Biden's Inauguration Day to once again try to rewrite the history of the last four years.

A military band played "All Hail the Chief" as Trump walked onto a small stage, lined with American flags, and up to a lectern bearing the presidential seal. He first praised his own family -- whom he put into positions of power, breaking with presidential norms -- and singled out first lady Melania Trump -- known for her privacy -- to say a few words.

"Being your first lady was my greatest honor. Thank you for your love and your support. You will be in my thoughts and prayers," she said.

Trump ticked off his accomplishments, spoke about the pandemic in past tense and predicted a boom in the stock market in the coming weeks, before offering a warning of the new administration -- without ever mentioning Biden's name.

"I hope they don't raise your taxes," Trump said, "but if they do, I told you so!"

He later added, "I wish the new administration great luck and great success. I think they'll have great success. They have the foundation to do something really spectacular."

"So just a good-bye. We love you. We will be back in some form," Trump vowed. "Have a good life. We will see you soon."

Trump is now headed on Air Force One to his resort in West Palm Beach, Florida, for the final time as president.