To replace a lost passport, the general process involves these main steps:

1. Report the lost passport immediately to the relevant authority. For the US, this is done by submitting Form DS-64 online or by mail to the State Department, to officially declare the passport lost or stolen. This invalidates the lost passport.
2. You must apply in person for a new passport using Form DS-11 (for the US). This requires an appointment at a passport acceptance facility such as a post office or passport agency, or at a U.S. Embassy or consulate if abroad.
3. Prepare the necessary documents, including:
   • Proof of U.S. citizenship (e.g., expired passport, birth certificate)
   • Valid government-issued photo ID
   • A recent passport photo meeting specified requirements
   • Social Security Number if applicable
   • Payment of applicable fees
   • Completed forms DS-11 and DS-64
4. Submit the application and documents in person at your appointment. The processing time generally ranges from 4 to 8 weeks, with an option for expedited service at additional cost.
5. If you are outside the U.S., report the loss to the local police and your nearest U.S. embassy or consulate. They may issue a temporary or limited-validity passport to get you home or allow onward travel.

This process varies slightly by country, but the key steps—reporting the loss, applying in person with proof of identity and citizenship, and submitting forms—are consistent. For example, the UK and Germany have similar requirements with local adaptations. In summary, replacing a lost passport involves prompt reporting, completing required forms, gathering identity and citizenship documents, applying in person at an authorized facility, and awaiting processing to receive a new passport.