Paternity is legal fatherhood—and establishing it is one of the most important steps in the child custody and support processes. A man is generally presumed to be the father of children born to his wife during their marriage. For unmarried parents, the biological father does not have legal rights to his child until paternity is established. Paternity may be established through a court-ordered paternity test, or by the father signing an acknowledgment of paternity (AOP). When paternity is established by one of these methods and the father is not the primary custodian or caretaker of the child, he will be ordered to pay child support.

In a case of mistaken paternity, a man who believes he is not the father of the child may file a petition (lawsuit), and the court may generally terminate the parent-child relationship and the man’s obligation to pay child support upon proof through genetic testing that he is not the father of the child.

The process of adding a father to a birth certificate is an important issue related to paternity.

In Wisconsin, paternity is the legal recognition of a man as the father of a child. When a child is born to married parents, the husband is presumed to be the father. For children born to unmarried parents, the biological father does not have legal rights until paternity is established. Paternity can be established by signing a voluntary Acknowledgment of Paternity (AOP) form or through a court-ordered paternity test. Once paternity is established, if the father is not the primary custodian, he may be required to pay child support. If a man has reason to believe he is not the biological father of a child for whom he has been identified as the father, he can file a petition to challenge paternity. Upon providing genetic test results that prove he is not the father, the court may terminate his parental rights and obligations, including child support. Additionally, establishing paternity is a necessary step for adding the father's name to the child's birth certificate.