The oath is found in Article II of the Constitution. It contains 35 words and goes as follows:
"I do solemnly swear (or affirm) that I will faithfully execute the Office of President of the United States, and will to the best of my ability, preserve, protect and defend the Constitution of the United States."
According to ABC News, George Washington reportedly added the words "so help me God" to the oath, and it has been since included by every president except Theodore Roosevelt.
All but two presidents placed their hand on a Bible while saying the oath, according to the Joint Congressional Committee on Inaugural Ceremonies. John Quincy Adams took the oath upon a book of the law. Theodore Roosevelt did not use a Bible for his first inauguration.
In 2013, President Barack Obama took the oath using two Bibles, one owned by Abraham Lincoln and the other by Martin Luther King Jr.
The vice president-elect takes a slightly different, longer oath, which is also utilized for members of Congress and some other federal employees:
"I do solemnly swear (or affirm) that I will support and defend the Constitution of the United States against all enemies, foreign and domestic; that I will bear true faith and allegiance to the same; that I take this obligation freely, without any mental reservation or purpose of evasion; and that I will well and faithfully discharge the duties of the office on which I am about to enter: So help me God."