The oath of office of the President of the United States is the oath or affirmation prescribed by the United States Constitution before the President begins the execution of the office. The wording is specified in Article II, Section One, Clause 8:

While the Constitution does not mandate that anyone in particular should administer the presidential oath of office, it is typically administered by the Chief Justice. There have been several exceptions, however. George Washington was sworn into office during his first inauguration, on April 30, 1789, by Chancellor of New York Robert Livingston. William Cranch, chief judge of the U.S. Circuit Court, administered the oath to Millard Fillmore on July 10, 1850, when he became president after the death of Zachary Taylor. Upon being informed of Warren Harding's death, while visiting his family home in Plymouth Notch, Vermont, Calvin Coolidge was sworn in as president by his father, John Calvin Coolidge, Sr., a notary public. Most recently, Federal Judge Sarah T. Hughes administered the oath of office to Lyndon B. Johnson aboard Air Force One after John F. Kennedy's assassination on November 22, 1963.