A Certificate of Citizenship (COC) is the document that proves citizenship. If you do not have a COC, you can [hyperlink https://www.uscis.gov/n-600 ]click here to apply[/hyperlink] for this document through the United States Citizenship and Immigration Services (USCIS) website. The National Council for Adoption provides additional details on this [hyperlink https://adoptioncouncil.org/wp-content/uploads/2021/01/Certificate-of-Citizenship-Factsheet-2021.pdf ]fact sheet[/hyperlink].