In contrast with prescriptions for law reform for unmarried cohabitants, this article studies legislative inertia on the subject. It compares France and the Canadian province of Quebec, drawing on theoretical treatment of boundaries from critical geography, queer theory, and sociolegal work on law reform. Abstinence from legislating for cohabitants has not secured legal stasis. Informally and indirectly, ad hoc responses to cohabitation have amended the boundaries of marriage and fundamental legal categories. A conservative approach to marriage and cohabitation has failed to conserve marriage. We identify a gap, not between law and social life but between law and its prevailing justification, that cohabitants are free to choose to marry or to conclude contracts. Legislative and judicial developments show that this justification fails to persuade. Finally, we read France and Quebec’s approach to cohabitation as symptomatic of an impoverished misreading of the civil law tradition.