This chapter addresses a topic that has been one of Bruno's main concerns both as an academic and as a judge: the potential for decentralized responses against infringements of community interests. This is one of international law's perennial topics underlying pieces on obligations erga omnes, actio popularis, and jus cogens, but also humanitarian intervention, third-party countermeasures, and transnational litigation. The chapter provides a broader - and necessarily cursory - perspective on their structural features: what is provided is a comparative evaluation of how the international legal system responds to assertions, by individual States, of a right to defend community interests and thereby to act as guardians of an international public order. It reviews a heterogeneous range of enforcement measures (legal proceedings before international courts, the exercise of national jurisdiction, and forcible as well as non-forcible coercive measures), and takes account of general international law as well as treaty-specific enforcement regimes. The overarching purpose of this exercise is to evaluate the potential, under contemporary international law, for what might be called 'public interest enforcement', and to assess the common features and weaknesses of the different legal concepts used to justify it.