In this paper, I introduce the concept of ‘big G’ and ‘small g’ gender to help conceptualise how actors in Victoria’s domestic and family violence (DFV) policy subsystem talk about and understand gender. Big G gender tends to be categorical, more fixed than fluid, and relates mainly to the state of being male or female. Small g definitions see gender as something constituted by actions, that resides both in individuals and in societal structures, and that refers to patterns of relationships within and between sex categories. I explain why such varied definitions of gender pose a problem for DFV advocates, and how big G definitions might be associated with reluctance to accept gendered explanations for DFV. Conversely, I show how small g definitions (coupled with an analysis of power in relationships) can help us understand both the way gender influences a variety of forms of DFV. This in turn helps us to understand how to address the problem.