Every four years here in the United States. Today is the Inauguration of Barack Obama as the 44th President of the United States. The Inauguration is where the President takes the oath of office.
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.
It is tradition for the Presidents to add the work "so help me God" at the end of the oath which is written in the Constitution of the United States.
Inauguration Day was first set for March 4th and in 1937 was changed by the Twentieth Amendment of the Constitution to January 20th. George Washington's Inauguration was held on April 30, 1789 in New York City. Traditionally the President takes the oath of office at the Capital in Washington, DC. The oath is administered by the Chief Justice of the United States.