N-400 Application for Naturalization

The N-400 form is the Application for Naturalization, used by lawful permanent residents (green card holders) who are eligible to apply for U.S. citizenship through the naturalization process. Naturalization is the process by which eligible immigrants become U.S. citizens.

The N-600 form is the Application for Certificate of Citizenship, used to obtain a certificate proving U.S. citizenship for individuals who acquired or derived citizenship through their parents.