Principles of international justice serve as aspirational goals, constraints, and evaluative criteria for the development of the institutions and practices of global environmental politics. In this chapter, these three roles will be considered in terms of the way that each shapes political treatment of international environmental issues. First, the notion of international justice itself will be explored, identifying controversies within the scholarly literature that contest the scope of justice as well as its application to environmental issues. Three conceptions of international justice will be described and briefly explored: an older sense based in post-Westphalian norms of state sovereignty; a newer but weaker sense based in the idea of universal human rights and concerned with providing all the requisite minimum resources or protections for those rights to be respected; and a stronger sense, based around the international extension of distributive justice principles and concerned with providing equitable access to key social and economic resources. These conceptions of justice will then be applied to several issues in global environmental politics to illustrate their scope and explore their implications, including global climate change and international fisheries management. Finally, some reflections on the strengths and limits of justice-based analyses of environmental problems shall be offered.