Paternity, as defined in the US legal arena, is the quality or state of being a father, or the male parent of a child. The legal obligations of being a father are established by consent to paternity and DNA testing. DNA testing is the best proof of paternity. The US Department of Health and Human Services says that every state in the US must offer unwed parents the chance to establish paternity by voluntarily signing an Authorization of Paternity Form (AOP, also known as the Paternity Acknowledgement form). The AOP establishes who has rights to a child.