Since George Washington first said the words on April 30, 1789, as prompted by Robert Livingston Chancellor of State of New York, every President of the United States has repeated the following simple presidential oath of office as part of the inauguration ceremony:

"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."

The oath is worded and administered in accordance with Article II, Section I of the U.S. Constitution, which requires that “Before he enter on the Execution of his Office, he shall take the following Oath or Affirmation:”

Of the three clauses in the Constitution that mention oaths of office, this is the only one that contains the exact words to be recited. Under Article I, Section 3, Senators, when assembled as a court of impeachment, do so “on Oath or affirmation.” Article VI, Clause 3 has been interpreted by the Supreme Court to mean that all federal and state executive, legislative, and judicial officers “shall be bound by oath or affirmation, to support this Constitution.” The presidential oath, however, goes far beyond the more general oaths in requiring new presidents to swear or affirm that they “will to the best of my ability, preserve, protect and defend the Constitution of the United States.” The only president confirmed as having vowed to “affirm” rather than “swear” was Franklin Pierce in 1853.

Who May Administer the Oath?

While the Constitution does not stipulate who should administer the oath to the president, this is typically done by the Chief Justice of the United States. Constitutional law experts agree that the oath could also be administered by a judge or official of the lower federal courts. For example, 30th President Calvin Coolidge was sworn in by his father, then a Justice of the Peace and notary public in Vermont.

Currently, Calvin Coolidge remains the only president to be sworn in by anyone other than a judge. Between 1789 (George Washington) and 2013 (Barack Obama), the oath has been administered by 15 Associate Justices, three federal judges, two New York state judges, and one notary public.

Hours after the assassination of President John F. Kennedy on November 22, 1963, U.S. District Court Judge Sarah T. Hughes became the first woman to administer the oath when she swore in Lyndon B. Johnson onboard Air Force One in Dallas, Texas.

Forms of Administering the Oath

Over the years, the presidential oath has been administered in two ways.

In one form now rarely used, the person administering the oath posed it in the form of a question, as in, “Do you George Washington solemnly swear or affirm that ‘you’ will …”

In its modern form, the person administering the oath poses it as an affirmative statement, with the incoming president repeating it verbatim, as in, “I, Barak Obama do solemnly ‘swear’ or ‘affirm that ‘I’ will …”

Use of Bibles

Despite the First Amendment’s “Establishment Clause” guaranteeing the separation of church and state, incoming presidents traditionally take the oath of office while raising their right hands while placing their left hands on Bible or other books of special – often religious -- significance to them.

U.S. President Barack Obama is sworn in as First lady Michelle Obama looks on. Alex Wong/Getty Images

John Quincy Adams held a law book, indicating his intention to base his presidency on the Constitution. President Theodore Roosevelt did not use a bible while taking the oath in 1901.

After George Washington kissed the bible he held while taking the oath, most other presidents have followed suit. Dwight D. Eisenhower, however, said a prayer rather than kissing the Bible he was holding.

Use of the Phrase ‘So Help Me God’

Use of “So help me God” in the presidential oath calls into question the constitutional requirement for separation of church and state.

Enacted by the First U.S. Congress, the Judiciary Act of 1789 explicitly required “So help me God” to be used in the oaths of all U.S. federal judges and other officers other than the president. In addition, the words of the presidential oath — as the only oath specifically spelled out in the Constitution — do not include the phrase.

While not required by law, most presidents since Franklin D. Roosevelt have added the phrase “So help me God” after reciting the official oath. Whether presidents before Roosevelt added the words is a source of debate among historians. Some say that both George Washington and Abraham Lincoln used the phrase, but other historians disagree.

Much of the ‘So help me God’ debate hinges on the two manners in which the oath has been given. In the first, no longer used manner, the administrating official frames the oath as a question, as in “Do you Abraham Lincoln solemnly swear…,” which seems to demand an affirmative response. The current form of “I do solemnly swear (or affirm)…” demands a simple response of “I do” or “I swear.”

In December 2008, atheist Michael Newdow, joined by 17 other people, plus 10 atheist groups, filed a lawsuit in the District Court for the District of Columbia against Chief Justice John Roberts seeking to prevent the Chief Justice from saying “so help me God” in the inauguration of President Barack Obama. Newdow argued that the 35 words of the Constitution’s official presidential oath do not include the words.

The District Court refused to issue an injunction preventing Roberts from using the phrase, and in May 2011, the U.S. Supreme Court refused Newdow's request to hear the case.

LBJ’s Air Force One Swearing-In Ceremony\

Vice President Lyndon B. Johnson is sworn in to the office of the Presidency aboard Air Force One in Dallas, Texas, hours after the assassination of President John F. Kennedy. Bettmann Archive/Getty Images

By far the most tragically bizarre presidential oath ceremony occurred aboard Air Force One at Love Field in Dallas, Texas, on November 22, 1963, when President Lyndon B. Johnson was sworn in hours after the assassination of President John F. Kennedy.

The oath was administered to Johnson in a hot and crowded Air Force One conference room by federal judge Sarah T. Hughes, marking the only time in history that the oath has been administered by a woman. Instead of a traditional Bible, Johnson held a Catholic missal that Secret Service agents had retrieved from Kennedy’s Air Force One bedroom.

After taking the oath, Johnson kissed his wife Lady Bird on the forehead. Lady Bird then held took Jackie Kennedy's hand, telling her, “The whole nation mourns your husband.”

What About the Vice President's Oath?

Under current federal law, the Vice President of the United States recites a different oath of office as follows:

“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.”

While the Constitution specifies that the oath taken by the vice president and other government officials states their intention to uphold the Constitution, it does not specify the exact wording of the oath.

Traditionally, the vice president’s oath has been administered by the Chief Justice on inauguration day on the floor of the Senate shortly before the president-elect is sworn in.

Notable Oath Gaffes

While it may seem to be a relatively simple process, delivering and responding to the presidential oath of office has not always gone smoothly. Some constitutional law experts contend that even accidental deviations from the proper script could invalidate the oath, and possibly even the legality of the presidency of the oath-taker.

In 1929, while delivering the oath to President Herbert Hoover, former president and then Chief Justice William Howard Taft read Hoover the words “preserve, maintain, and defend the Constitution,” instead of “preserve, protect, and defend the Constitution.” Schoolgirl Helen Terwilliger, listing to the ceremony on the radio, caught the error and reported it to her local newspaper. Though he eventually admitted to having made the mistake, Chief Justice Taft declared that it had not invalidated the oath and thus a do-over by Hoover was not necessary.

During the swearing-in of President Harry S Truman in 1945, Chief Justice Harlan Stone mistakenly started the oath by saying, “I, Harry Shipp Truman, …” In fact, the “S” in Truman’s name is not an initial, but his entire one-letter middle name, a compromise reached between his parents to honor both of his grandfathers, Anderson Shipp Truman and Solomon Young. Truman caught the error and without skipping a beat responded, “I, Harry S Truman, ...”

In 1973, President Richard Nixon, despite having recited the line correctly during his first inauguration in 1969, added the word “and” between “preserve” and “protect”, resulting in “preserve and protect, and defend the Constitution of the United States.”

In 2009, a mistake during the oath forced President Barack Obama to be sworn-in twice. During Obama’s first-term inauguration on Tuesday, January 20, 2009, Chief Justice John G. Roberts prompted “… that I will execute the Office of President to the United States faithfully,” instead of “… that I will faithfully execute the office of President of the United States.” After hesitating as he waited for Roberts to correct the mistake, Obama repeated his initial, incorrect prompt. While constitutional experts insisted it was not necessary, Obama, already weary of conspiracy theories regarding his qualifications to serve, had Roberts re-administer the oath correctly the next day in the White House.