Paternity law refers to body of law underlying legal relationship between a father and his biological or adopted children and deals with the rights and obligations of both the father and the child to each other as well as to others. A child's paternity may be relevant in relation to issues of legitimacy, inheritance and rights to a putative father's title or surname, as well as the biological father's rights to child custody in the case of separation or divorce and obligations for child support.

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Under common law, a child born to a married woman is presumed to be the child of her husband by virtue of a "presumption of paternity" or presumption of legitimacy. In consideration of a possible non-paternity event (which may or may not include paternity fraud) these presumptions may be rebutted by evidence to the contrary, for example, in disputed child custody and child support cases during divorce, annulment or legal separation.