Every president, including George Washington, has taken the oath of office.

The first presidential oath was: "I do solemnly swear or affirm that I will support the Constitution of the United States."

During the Civil War, the oath was expanded to include the phrases "support and defend the Constitution... against all enemies, foreign and domestic" and to bear "true faith and allegiance."

While most presidents swear their oath of office on the Bible, a few have chosen to use law books instead. 

Regardless, a sworn oath made before the people and God remains a binding word of honor.