To what extent, and in what ways, is judicial review shaped by its specific constitutional context? Recent developments in Australian judicial review of administrative and adjudicative powers may be of some interest in exploring this terrain. This paper discusses the impact of Australia’s basic law, the Constitution, on judicial application of a concept central to judicial review: invalidity. It argues that the full impact of the separation of judicial power in Australia’s Constitution on thinking about the status of “invalid” decisions has yet to be revealed; and indicates some potential areas where doctrinal adjustments may be necessary to reflect and integrate the ‘constitutionalised’ role of invalidity.