The Swearing-in of the President

The swearing-in of the President of the United States occurs upon the commencement of a new term of a President of the United States. United States Constitution mandates that the President make the following oath or affirmation before he or she can "enter on the Execution" of the office of the presidency: 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 swearing-in traditionally takes place at noon on Inauguration Day at the United States Capitol in Washington, D.C., with the Chief Justice of the United States administering the oath. Until 1937, Inauguration Day was March 4. Since then, Inauguration Day has occurred on January 20 (the 1933 ratification of the Twentieth Amendment changed the start date of the term).
(http://en.wikipedia.org/wiki/Inauguration_Day)