For more than thirty years, the central questions of the law of parentage have been when and to what extent determinations of legal parenthood should be based on biological relationship, marriage to a child’s biological parent, or functioning as or intending to be a parent. In Obergefell v. Hodges, the Supreme Court endorsed the claim that children whose parents are married are better off socially and legally than nonmarital children; its language could easily be taken to support legal rules that encourage or prefer childrearing within marriage. On the other hand, the Court’s argument assumes that the same-sex couple—both members—are in fact parents of the children, even though it is highly likely that only one adult is biologically related to child. The unspoken premise of the argument is that both are parents because both function as parents (and often, but not always, both participated in the decision-making process that led to the children’s conception and birth).

Today it is generally agreed that the law should protect relationships between children and adults who are committed to the children’s welfare, and who have taken on the responsibilities of parenthood; the debate is over the best way to protect children and to advance other social goals. This Article examines how the law in the various states balances claims to base legal parentage on biology, function, and marriage and how the Supreme Court’s same-sex marriage decisions are affecting that balance. It concludes that the decisions are having some impact in the lower courts, particularly by supporting recognition of the parental claims of adults who are not biologically related to children whom they have raised with their same-sex partners. However, these decisions are limited and cannot protect children and their functional parents adequately in all situations. Therefore, legislative solutions are still needed.