The interpretation given by the courts to the word ‘matter’ in sections 75 and 76 of the Commonwealth of Australia Constitution, and the restrictive approach taken by the courts to what amounts to a sufficient interest in a matter, have led to the consequence that only litigants who can demonstrate a personal interest can bring an action to challenge a breach of the Constitution. This provides insufficient protection for constitutionalism because it means that the enforcement of the Constitution is contingent on there being a self-interested applicant who will bring an action – and, conversely, creates the risk that breaches of the Constitution will be allowed to stand in cases where those who do have standing find it in their political interests to refrain from taking action. With its focus on personal interest, the current approach excludes the altruistic applicant and runs counter to the theory that all citizens have a right to ensure that the Constitution is complied with. This paper examines the way in which the actio popularis of Roman law served the ideal of the engaged citizen by enabling citizens to initiate legal action to enforce public duties, and how modern equivalents of the actio in a number of jurisdictions achieve the same purpose. The paper draws on John Rawls’ theory of justice in arguing for reform of the law on standing in Australia so as to confer open standing in constitutional cases.