The significance of the Bible Joe Biden is using on Inauguration Day

When President-elect Joe Biden takes the oath of office Wednesday, he'll do so using a Bible with 127 years of family history behind it.

Biden, who is Catholic, has used the leather-bound, 5-inch thick book, which has been in his family since 1893, each time he's been sworn into elected office during the course of his career.

Inscribed inside are the dates of each of his swearing-in ceremonies. Biden's late son Beau also used the family Bible when he was sworn in as Delaware's attorney general.

"Every important date is in there," Biden told television host Stephen Colbert in December.

Being sworn in on a Bible is not required by the Constitution, but modern-day presidents have adhered to tradition and chosen symbolic Bibles for their inauguration days.

The tradition itself dates back to President George Washington, who was sworn in using a Masonic Bible in 1789.

Vice-President elect Kamala Harris will be sworn in using multiple Bibles, each of which has personal significance.

One is the family Bible of civil rights icon Rosa Parks, a large heavy clothbound book, published in 1900. Other Bibles chosen by Harris include one that belonged to Thurgood Marshall, the first Black Supreme Court Justice, who Harris has said inspired her career path, and a Bible that belonged to a close family friend, Mrs. Regina Shelton.

"When I raise my right hand and take the oath of office tomorrow, I carry with me two heroes who’d speak up for the voiceless and help those in need: Justice Thurgood Marshall and Mrs. Shelton," Harris wrote on Twitter Tuesday.

ABC News' Chad Murray, Averi Harper and Beatrice Peterson contributed to this report.