This thesis assesses the relationship between transnational socioeconomic justice and the World Trade Organization (WTO). It addresses three main sets of questions. First, how is the currently dominating dichotomous approach to tackling the problem of justice beyond state borders inadequate; and how might its inadequacies be addressed by going beyond such an approach? Second, what kind of normative principles should be satisfied in the context of the WTO so that the multilateral trading system fulfils relevant demands of fairness and justice? Third, how can the fulfilment of these principles be improved? This thesis thus analyzes the relationship between justice and the WTO from a dual perspective: it explores both what the existence of the WTO implies for theories of justice beyond state borders and how normative political theory helps to address governance challenges in the context of the WTO. The thesis thereby contributes to the literature on transnational socioeconomic justice, the normative assessment of international trade, above all in the context of the WTO, and the ongoing debate about reforming the multilateral trading system. The thesis has three main parts. The first part addresses the nature of principles of socioeconomic justice. It examines procedural and substantive principles as well as comparative and non-comparative principles in light of current debates about commutative, distributive and sufficientarian justice. In the context of the WTO, this thesis makes the case that substantive principles of a comparative nature matter in the international arena even if we were to initially restrict our attention to sufficientarian justice and to ostensibly procedural principles of commutative justice. The second part focuses specifically on substantive principles of socioeconomic justice beyond state borders. It critically discusses the current theoretical landscape and develops and defends a novel conceptual framework for the scope and site of justice. The third part assesses the WTO from a normative point of view in light of the theoretical lens set out in the second part. It argues that the WTO qualifies as a subject of socioeconomic justice, discusses the specific normative standards this entails and assesses the potential and limits of realizing these standards in practice, above all in the context of developing countries in the WTO.