The Oath of Allegiance is the final step before you become a U.S. citizen. When USCIS approves your Form N-400, Application for Naturalization, you will have to attend a ceremony and take the Oath of Allegiance. In fact, you are not a U.S. citizen until you take the oath. At the ceremony it’s required to surrender your green card, instead you will receive a Certificate of Naturalization. The certificate is a proof of your U.S. citizenship. After receiving it you should update your citizenship status in your Social Security record and request a U.S. passport from the U.S. Department of State.