Abstract: This paper looks at our new technological ability to determine genetic paternity, in the context of legal and social developments related to the family, and tries to come up with some guidelines for figuring out how to decide parentage in the modern era. Many claim that since DNA tests mean we can now easily tell who the genetic father is, we should make that man the legal father and release any other who might be playing that role from parental responsibility. However the trend in law over recent decades has been in the direction of reducing the role that biology plays in determining parentage, with the law giving increasing deference to existing social parenting relationships and to the intent to create such relationships as factors to take into account when parentage is contested. This paper assesses the importance of the genetic link to parenting, considers it in comparison to a variety of other factors relevant to parenting, and sets out some guiding principles for choosing among possible parents, principles designed to serve children's interests in stable, nurturing, parenting relationships.