Illegitimacy was a term in common usage for the condition of being born of parents who are not validly married to one another; the legal term is bastardy. That status could be changed (in either direction) by civil law or canon law (see Princes in the Tower for an example of the former). In some locations, marriage of an illegitimate child's parents after his or her birth results in his or her legitimation.

In many societies the law did not (or does not) give illegitimate persons the same rights of inheritance as legitimate ones, and in some, not even the same freedoms. In England as late as the 1960s, for example, illegitimacy carried a strong social stigma among both middle and working class people, as it also did in the United States. As recently as the 1940s and 1950s there, unwed mothers were strongly encouraged to give their children up for adoption. Oft times, an illegitimate child would be raised by grandparents or married relatives as the "sister" or "nephew" of the unwed mother, just as in medieval and Renaissance Europe priest's children (especially bishop's and pope's children) were usually called their "nephews," giving us the term "nepotism". In those cultures the fathers of bastard children did not incur the same censure nor, generally, much legal responsibility, due both to social attitudes about sex and the difficulty of determining the father of a child with any degree of accuracy.

By the latter third of the 20th century in the U.S., all the states had adopted uniform laws that codify the responsibility of both parents to provide support and care for a child regardless of their parents' marital status and giving illegitimate (and adopted) persons the same rights to inherit their parents' property as anyone else. Generally speaking in the United States illegitimacy has been supplanted by the concept "born out of wedlock". One does not speak of a child being illegitimate; all children are equally legitimate.

Stating that a child is less entitled to civil rights, or in a state of sin, due to the marital status of his/her parents would be seen as highly controversial by even the most conservative people in the West today. Many religions still view extramarital or premarital sexual intercourse as a sin, but they generally feel that any resultant child is not in any state of sin.

Today the word "bastard" remains:

• a pejorative epithet. However, the word has been "reclaimed" by Bastard Nation, an advocacy group for the rights of formerly adopted children. In addition, the word is often used as an epithet, but without its pejorative sense, in Australian English - it is sometimes called the great Australian endearment.
• an acceptable adjective for describing odd-sized objects or parts, such as bolts with non-standard threads. There is a particular type of engineer's coarse file known in the trade as having a bastard cut, and referred to as a bastard.

Due to the common use of the word as a mildly profane generic insult for a man, many students are surprised to find that the use of the word to refer to a child of unmarried parents, for example Shakespeare's John the Bastard, is seen as appropriate by their teachers.

Parental responsibility

In the UK the notion of bastardy was effectively abolished by the introduction of The Children Act 1989 (which came into force in 1991), by virtue of introducing the concept of parental responsibility which ensures that a child can have a legal father even if that child's parents weren't married. However it was not until December 2003, with the implementation of parts of The Adoption and Children Act 2002 (http://www.hmso.gov.uk/acts/acts2002/20020038.htm), that parental responsibility was automatically granted to fathers of children born out of wedlock, and even then, only if the father's name appears on the birth certificate.