In common law, legitimacy is the status of a child born to parents who are legally married to each other; and of a child who is born shortly after the parents' divorce. In canon and in civil law, the offspring of putative marriages have been considered legitimate children. Analogously, illegitimacy is the status of a child born to unmarried parents; contemporary usage of the term illegitimate child is infrequent, even in legal usage, example euphemisms are extramarital child and love child. The concept of legitimacy was formerly of great consequence, in that only a legitimate child could inherit the estate of the father. In the United States, in the early 1970s, a series of Supreme Court decisions abolished most common-law disabilities imposed upon bastardy (illegitimate-child status), as violations of the Equal Protection Clause of the Fourteenth Amendment to the United States Constitution.

In April 2009, the National Center for Health Statistics announced that nearly 40 percent of American infants born in 2007 were borne by an unwed mother; that of 4.3 million children, 1.7 million were born to unmarried parents, a 25 percent increase from 2002. In Europe, there is a like increment in the number of extramarital children; in Bulgaria, France, Scotland, Wales, Slovenia, and Sweden, more than 50 percent of the children born in 2007 were extramarital. In parts of England, the Netherlands, Denmark, Austria and the Czech Republic more than 50 percent of first-born children were born extramaritally.