International legal scholarship is concerned with the fragmentation of international law into specialised legal systems such as trade, environment and human rights. Fragmentation raises questions about the inter-systemic interaction between the various specialised systems of international law. This study conceptually focuses on the interaction between World Trade Organisation (WTO) law and external international law. It introduces a legal theory of WTO law, constrained openness, as a way to understand that interaction. The idea is that WTO law, from its own internal point...