Legitimacy, in traditional Western common law, is the status of a child born to parents who are legally married to each other, and of a child conceived before the parents obtain a legal divorce. Conversely, illegitimacy (or bastardy) is the status of a child born outside marriage.
Depending on the cultural context, legitimacy can affect a child's rights of inheritance to the putative father's estate and the child's right to bear the father's surname or title. Illegitimacy has also had consequences for the mother's and child's right to support from the putative father. See Affiliation (family law).
As of 2012, the proportions of children born outside marriage, taking the median across countries, range from some 66% in Latin America to 40% in the United States and the European Union, and some 5% in East Asia. In addition, the illegitimacy rate in Western societies is increased slightly by 1-2% of children who were ostensibly born to couples but were in fact covertly conceived by a different biological father.
In medieval Wales, a "bastard" was defined simply as a child not acknowledged by its father. All children, whether born in or out of wedlock, that were acknowledged by the father enjoyed the same legal rights, including the right to share in the father's estate.
England's Statute of Merton (1235) stated, regarding illegitimacy: "He is a bastard that is born before the marriage of his parents." This definition also applied to situations when a child's parents could not marry, as when one or both were already married or when the relationship was incestuous.
The Poor Law of 1576 formed the basis of English bastardy law. Its purpose was to punish a bastard child's mother and putative father, and to relieve the parish from the cost of supporting mother and child. "By an act of 1576 (18 Elizabeth C. 3), it was ordered that bastards should be supported by their putative fathers, though bastardy orders in the quarter sessions date from before this date. If the genitor could be found, then he was put under very great pressure to accept responsibility and to maintain the child."