Koseki
戸籍 (こせき)
The Japanese family register system that officially records births, marriages, deaths, and names, serving as the primary legal document for identity and family relationships.
Koseki (戸籍) is Japan's family register system, a comprehensive legal record maintained by municipal governments that documents every Japanese citizen's identity, family relationships, and vital events. Unlike individual-based systems such as birth certificates in many Western countries, the koseki is organized by household (ko, 戸), with each family unit sharing a single register.
Naming Regulations Through Koseki
The koseki system is the primary mechanism through which the Japanese government regulates personal names. Municipal clerks review birth registrations and will reject names containing kanji not found on the approved jōyō or jinmeiyō kanji lists. Until the 2023 legal revision, the koseki recorded only the kanji of a name without its reading (furigana), meaning the official record contained no indication of pronunciation. The new requirement to include furigana addresses long-standing administrative challenges.
Broader Significance
The koseki system shapes Japanese naming in ways that extend beyond character restrictions. Married couples must choose one shared surname to register under, a policy that in practice means 96% of women adopt their husband's name. The system also governs adoption, divorce, and name changes — all of which require formal koseki amendments. For Japanese citizens, the koseki is the authoritative source of their legal identity, and obtaining a koseki tōhon (certified copy) is required for passports, marriage, and many official procedures.