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 Kansas, paternity is crucial for establishing a father's legal rights and responsibilities towards a child. If a child is born during a marriage, the husband is presumed to be the legal father. For children born to unmarried parents, the biological father does not have legal rights until paternity is established. This can be done voluntarily by signing an Acknowledgment of Paternity (AOP) or through a court-ordered DNA test. Once paternity is confirmed, if the father is not the primary caregiver, he may be required to pay child support. In cases where a man has been identified as the father but believes he is not, he can file a petition to challenge paternity. If genetic testing proves he is not the biological father, the court may terminate his parental rights and child support obligations. Additionally, establishing paternity is necessary for adding the father's name to the birth certificate, which has significant legal and social implications.