夫婦同姓 (mandatory shared surname)

Japan's legal requirement (Civil Code Article 750) that married couples share a single surname (夫婦同氏 or 夫婦同姓) — almost always the husband's, in practice. Rooted in the Meiji-era 民法 and unchanged despite repeated reform debates, making Japan the only G7 country still mandating this. The pre-marriage surname is called 旧姓 ('former surname'); women retaining 旧姓 in professional life is increasingly common. A frequent flashpoint in discussions of gender equality and family law.