A koseki (Japanese: 戸籍) or family register is a Japanese family registry. Japanese law requires all Japanese households to make notifications of their vital records (such as births, adoptions, deaths, marriages and divorces) to their local municipal authority. Domestic aspects such as marriages, divorces, acknowledgements of paternity of non-marital children, and adoptions, are only legitimized if they are recorded on the koseki. Births and deaths become legally effective as they happen, but such events must be filed by family members or other persons as allowed by law.
Koseki registration is required for all Japanese citizens, and possessing one is definitive proof of Japanese nationality, unless a renunciation application has been filed and recorded on the koseki for reference. In addition to koseki registration, Japanese citizens are also required to file a notification of residence, which is then recorded in the jūminhyō (住民票). Foreign residents, who cannot have a koseki, are only required to file a notification of residence and have a jūminhyō.