abstract. A fatal conflict in the legal definition of family lurks at the intersection of family law and zoning law. Family law doctrines have increasingly embraced the claims of “functional families”—those whose bonds can be traced to cohabitation and shared domestic life. At the same time, zoning laws have narrowed to recognize only formal families, effectively restricting residency to individuals related by blood, marriage, or adoption. As a result, family law’s “functional turn” remains vulnerable in at least thirty-one states. Using original legal analysis and historical research, this Note illuminates that contradiction, explains how it arose, and argues that it must be resolved to protect diverse family forms. This Note surveys the “functional turn” in state family law and develops a novel historical account of the shifting definition of family in zoning law, documenting its “formal turn.” It then offers normative and practical reasons why the definition of family should be loosened, offering recommendations for legislative and judicial reform.

author. Yale Law School, J.D. expected 2020; Yale University, Department of History, Ph.D. expected 2022. I am deeply grateful to Reva Siegel and David Schleicher for supporting this project from the beginning, through innumerable conversations and drafts. I also owe a special debt of gratitude to Douglas NeJaime for his generosity and guidance in shaping the result. Further thanks to John Witt, Joanne Meyerowitz, Serena Mayeri, Rachel Luban, Thomas Scott-Railton, Nina Varsava, Nick Werle, and the Yale Research Initiative in the History of Sexualities Writing Group for reading drafts and offering invaluable feedback along the way. Finally, my thanks to Matt Nguyen and the Yale Law Journal for terrific suggestions and careful editing. All errors are my own.