You can get a U.S. passport on the same day, but it typically requires making an appointment at a passport agency or center. Same-day service is usually only available for urgent travel needs, such as a flight within 14 days. You'll need to provide proof of your travel plans and bring the necessary documents, including a completed application form, passport photo, and payment. It's a good idea to call ahead and confirm availability, as walk-ins might not be accepted.