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 New Mexico, 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 typically 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 either voluntarily by signing an Acknowledgment of Paternity (AOP) or involuntarily through a court-ordered DNA test. Once paternity is confirmed, the father may be required to pay child support if he is not the primary custodian. In cases where a man has been mistakenly identified as the father, 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 obligations, including child support. Additionally, establishing paternity is necessary for the father's name to be added to the birth certificate. The state's statutes and family law code outline the specific procedures and rights associated with paternity.