Modern law allows some adults to agree among themselves on allocating parenthood through adoption, preconception agreements, surrogacy, and voluntary acknowledgments. These doctrines cannot be justified by the adults’ intentions, promises, contracts, or similar social conventions. Those powers rest on agents’ authority over their own lives; no one can have a personal right to decide who will control a child’s life. However, liberal justice requires such legal authority. Many reasonable citizens value childrearing irrespective of biological ties and should have a derived liberty to pursue families. Excluding citizens from parenthood denies them fair equality of opportunity. Modern parentage agreements empower nonbiological parents to build families in ways that respect themselves, the child, and other parents. Adoption empowers an adult to create parenthood through an express commitment, subject to state oversight to protect the child and existing parents. Second-parent adoption and acknowledgments of parentage enable a single parent and their partner to agree to share parenthood prospectively, which prevents subordination in familial projects, protects the child’s relationships, and facilitates equality for lesbian and gay adults. Preconception agreements do likewise for a gestational parent and their partners. Well-designed regulations may render gestational surrogacy consistent with equal respect for the surrogate and women generally.