The passport is the document that identifies you as a U.S. citizen. You must have a passport to enter a foreign country.
To apply for a passport, you will need to submit the completed application, two identical passport photos, a certified copy of your birth certificate, and the application fee. For a complete list of requirements and to download an application, please visit: http://travel.state.gov/passport. Allow at least three months for processing of your application.
If you already have a passport, check the expiration date. Your passport should be valid for six months beyond the date of your overseas stay.
Once you receive your passport, be sure to sign it immediately. It is not valid without a signature. Before leaving the U.S., make at least two copies of your passport and leave one copy at home and take one copy and the original with you. Should your passport be lost or stolen, present a copy of the passport to the U.S. Embassy when requesting that your passport be reissued. This will help speed up the re-issuing process.