Single family zones are ubiquitous, diversely-defined and both popular and controversial. Much of the controversy stems from who is excluded from living in these zones by the definition of “family.” After reviewing single family zones, policy rationales for them, and the basic types of definitions of family, this article surveys contemporary policy challenges and legal limits to definitions of “family.” Recognizing localities’ diverse contexts, the article articulates how localities can reassess their definitions and identifies relevant considerations.