This paper analyses how the size and socio-economic diversity of their electorate affect parliamentarians’ legislative behaviour. We study the Australian senate, which wields considerable legislative influence and is marked by large differences in the size and socio-economic makeup of the districts that senators represent. We demonstrate that as the size of their district increases, senators ask more questions and introduce more bills and amendments. By contrast, senators become less active as the diversity of their electoral district increases. The paper thus establishes that size and diversity of electorates have significant effects on legislative behaviour.