When a baby is born, there is almost never a debate about who that child's mother is. However, it can be more difficult to determine who that child's biological father is. When a couple is married, the woman's husband is presumed to be the baby's father, but in some cases DNA testing is necessary to determine paternity. Establishing paternity is important because it gives fathers rights to see and know their children. Before paternity is established, the mother may have control over child custody issues.
The governing law on paternity -- including DNA testing, legitimation requirements to establish visitation and custody, establishing a father's identify to receive child support and so forth -- is decidedly state law, with processes and requirements varied among jurisdictions and unique to each state.