The main family law of Japan is Part IV of . The contain provisions relating to the and notifications to the public office. Background The ie (家) or "household" was the basic unit of Japanese law until the end of World War II: most civil and criminal matters were considered to involve families rather than individuals. The ie was considered to consist of grandparents, their son and his wife and their children, although even in 1920, 54% of Japanese households already were nuclear families. This system was formally abolished with the 1947 revision of Japanese family law under the influence of the allied occupation authorities, and Japanese society began a transition to a more Americanized nuclear family system. However, the number of nuclear families only slightly increased until 1980, when it reached 63%, and the Confucian principles underlying the "ie" concept only gradually faded and are still informally followed to some degree by many Japanese people today. Marriage Marriage of Japan's formality takes the form of civil marriage. A marriage is effected by filing notification of it. A wedding ceremony performed by a religious or fraternal body is not a necessary element for a legal marriage. According to Articles 731–737 of the Civil Code, A man before attaining 18 years of age, a woman before attaining 16 years of age, may not marry. (Article 731) A minor shall obtain the consent of at least one parent to marry. (Article 737) Bigamy is prohibited. (Article 732) [declared unconstitutional in 2016 by the Supreme Court: A woman may not remarry within 6 months of the day of dissolution or cancellation of the previous marriage, except the case in which she both gets pregnant before the day and gives birth to the child. #1 (Article 733)] Lineal relatives by blood, collateral relatives within the third degree of kinship by blood #2, may not marry, except between an adopted child and their collateral relatives by blood through adoption. #3 (Article 734) Lineal relatives by affinity may not marry. #3 (Article 735) An adoptive parent or a lineal ascendant of an adoptive parent may not marry with an adopted child, their spouse, their lineal descendant, or a spouse of their lineal descendant. #3 (Article 736) It is considered that this remarriage prohibition is to avoid confusion as to the identification of the child's father. between one and one's sibling, uncle, aunt, nephew, niece by blood.