Japanese civil law and the official family registry system strictly require married couples to share a single unified surname under the legal concept of夫婦同姓, meaning both partners must choose either the husband's or the wife's family name upon marriage. Consequently, individuals cannot legally hold two official surnames simultaneously on their official government identification documents or family registries. While people can choose to use professional or maiden names in informal social settings, workplaces, or academic publications, legal documents, passports, and bank accounts must reflect the single designated family name recognized by Japanese civil registration laws.