唐代的養子法依古禮而制訂，只許收養同宗昭穆相當者，並例外地聽養三歲以下棄兒；養女因不涉及傳承問題，態度上比較開放。為了維護身分秩序，養子法不准別色相養。由於養子法不能滿足人們的需求與期望，一些非法的、不合禮法的收養形式遂相應而生。大致來說，唐人的收養行為以同宗養子、異姓養子、養女、養賤人為子女四大類型為主，另有收養隨母嫁子女、宦官養子女之特殊形態。禮法與人情之間的落差是很大的。養子涉及身分的改變與家族秩序的重建，也影響其在養家、本生家的地位與關係，故相關規定很嚴格，民間習俗也有慣常作法。養子依親子孫法，異姓者要改姓，譜系上要列於養家，戶籍要析出本生籍。服紀上要尊所後，降本服一等；財產方面，養子一如親子之分額；在政治權力上，養子可以襲封與承蔭。養子是一種擬血緣關係，如本生家無子，或養父母不願留養，養子可歸宗。養子一旦歸宗，收養關係便終止，所有禮法地位與權利義務關係皆回歸如常。

The child adoption regulations of the Tang Dynasty were set up in accordance with ancient formalities. The regulations allowed only children of the same clan and of the same position in the family tree to be adopted, except for the adoption of abandoned children under three years of age. The regulations were more relaxed towards adopted daughters because there were no issues of inheritance in such cases. To maintain the social statuses and identities of the families, the child adoption regulations did not allow respectable people to adopt disreputable people or vice versa. However, some illegal ways of child adoption appeared because the child adoption regulations were unable to meet the needs and expectations of all people. In general, there existed four types of child adoption in the Tang Dynasty: adoptive children of the same clan and of the same position in the family tree; adoptive children with a different surname; adoptive daughters;
and adoptive children of disreputable origins adopted by respectable families. In addition, there were other special types of child adoption, such as husbands adopting stepchildren and eunuchs adopting children. There was an appreciable gap between the government regulations and the interests of the society.Child adoption involved the change of the child’s identities and the reconstruction of the adoptive family’s genealogy. It also affected the familial and legal statuses as well as the relations and positions of adopted children in their birth families and adoptive families. Therefore, the relevant regulations were very strict and the folk customs also affected the common practices. Like birth children, adopted children had to use their adoptive parents’ surnames, list their names in their adoptive
families’ genealogical tables, and remove themselves from the household
registration of their birth families. For the mourning apparel system, the mourning apparel adopted children wore for their adoptive parents had to be the same as their siblings in the adoptive family; and the mourning apparel they wore for their birth parents had to move down by one rank. As for property, adopted children might receive their share as if they were birth children. For political rights, adopted children could inherit fiefs and titles of nobility. Child adoption is a mimic kinship. If birth families did not have children or adoptive parents did not want to keep their
adopted children any more, the adopted children could return to their birth
families. Once adopted children went back to their birth families, the adoptive relationships ceased, and all familial and legal statuses, and rights and obligations returned to the states prior to adoption.