During the early and middle decades of the twentieth century, a number of jurisdictions introduced specific laws to deal with the crime of infanticide, following the English approach to this offence which allowed for a reduced conviction and flexible sentence in cases where women killed their babies aged under 12 months whilst in a mentally disturbed state. Taking the Irish experience, this paper explores the role of social norms in the criminal justice response to infanticide. It is argued that, irrespective of the existing legal framework in place, implicit shared social norms about the ‘appropriate’ outcome in cases where women killed their babies played a crucial part in how this crime has been dealt with by the courts. The criminal justice response will be assessed against shifting legal and social environments, in particular, the enactment of a specific Infanticide Act in 1949, and Ireland's transition from a conservative to a liberal society during the last decades of the twentieth century. In particular, the role of social norms in the interpretation of the medical rationale for this law is explored, and the impact of Ireland's social and cultural liberalisation on the criminal justice response to infanticide is examined.