The Acknowledgment of Paternity (AOP) is a legal form that parents who are not married to each other use to establish paternity. Paternity means legal fatherhood. When both parents sign an Acknowledgment of Paternity and it is filed with the Texas Vital Statistics Unit, the biological father becomes the legal father. Once the biological father becomes the legal father, he has all the rights and duties of a parent, including his name being placed on the birth certificate. Signing the AOP is voluntary. Parents who would like to establish paternity for their child using the AOP must seek the assistance of an AOP certified entity, which may be found at a local hospital or a local child support office.