Legal scholars and social scientists are increasingly calling on legislators, lawyers, and judges to recognize and embrace expanding definitions of the family. Implicit in such calls is the expectation that legal recognition of expanding definitions of the family will protect children's attachment relationships with adults, irrespective of their biological ties to those adults. Through a detailed, historical examination of custody decisions in disputes between biological and nonbiological parents in the state of Iowa, this research suggests that judicial recognition of more expansive definitions may not result in decisions that protect children's attachment relationships. This is true because the legal impact of family definitions appears to be contingent upon cultural and political factors that may undermine the expected effects of changing definitions. This research also suggests that judicial recognition of children's rights may be the most apt way to promote legal changes that will protect children's attachment relationships.