 Legal parenthood consists in possessing legal parental rights and responsibilities. Historically, in the US, a pregnant woman’s husband has been presumed to be her child’s legal father: marriage, not biology, underpins the legal relation. This has faced legal challenges from genetic fathers (Rosenman 1995; see Hubin 2003 on fatherhood). Law in different jurisdictions is also increasingly recognizing legal parental rights on the basis of same-sex marriage. The rise of ART has prompted many questions regarding assignment of legal parenthood when there are contending claims—as between a couple who commissioned a contract pregnancy and the contracting gestational parent. They have also stretched the understanding of parenthood, as when the Ontario Court of Appeal recognized three legal parents (A.A. v. B.B., 2007 ONCA 2)—a lesbian couple and sperm donor. The wider use of ART and gamete donation, along with broader recognition of same-sex marriage and changing social attitudes towards polyamory, have led some philosophers to argue for rethinking the family to include more than two social and legal parents, on grounds including child welfare, social justice, and environmental impact (see, e.g., Cutas 2011, Shrage 2018, Gheaus 2019, Grill 2020).