Marriage law is often conceptualised as an instrument of power that illegitimately imposes the will of the State on its citizens. Paradoxically, marriage law is also offered as a route to liberation. In this thesis, I question the efficacy of this type of analysis by investigating the actual power effects of marriage law. Using Michel Foucault’s concepts of bio-power and government, and his genealogical approach to history, I identify the role played by marriage law in governing the social domain over a discrete period of Irish history. Drawing on this analysis, I suggest that marriage law is part of a dense network of power relationships that cannot be reduced to a binary relationship of oppression and liberation. Rather, marriage law acts, in conjunction with other techniques of government, to conduct conformity in social behaviour. Until the 1960s, marriage was considered a fully social matter outside the jurisdiction of politics. With the adoption of a Keynesian economic model at the end of the 1950s the welfare of the population became a matter of political concern. In the 1970s, the vulnerable dependent wife emerged as an object of regulation and marriage law was enacted to protect her through enforcement of the obligations of morally bound, gendered, lifetime marriage. The need to protect this form of marriage drove further reform of marriage law in the 1980s and divorce legislation enacted in 1997. An increasingly rationalised, economic approach to government, adopted following ratification of the Maastricht treaty, required the deployment of social scientific knowledge by government. Within the domain of family life, science connected social stability to relationship stability. Marriage law reform in the 2000s, therefore aimed to promote stability in relationship behaviour by acknowledging, regulating, and promoting relationship practices that performed lifetime marriage. Over the research period, marriage law operated as one among many techniques of government that installed a detailed apparatus of surveillance and control around individual lives, with the objective and effect of conducting conformity in relationship behaviour.