In this thesis, I present a model that uses the legal relationship of marriage to spur an increase in specialization of the couple's division of labor. Marriage offers protection if a member of the couple chooses to specialize in household labor in the event that the relationship ends. While that spouse faces a lower wage upon re-entering the workforce, due to the loss of human capital, marriage provides a legal claim on the income of the market-specializing spouse and the property accumulated during the relationship. That is, marriage reduces the risk facing a household-specializing spouse in the case of divorce or their spouse's death. For couples who cannot marry, there is no such protection and the risk to specializing is high. Data from married same-sex couples in Massachusetts and cohabiting same-sex couples in states without same-sex marriage provide initial support for the hypothesis that marriage increases specialization.