International trade law is particularly prone to tensions with other areas of global governance given how trade rules interact with public policies addressing environmental and social problems linked to expanding economic activities. This chapter explores how the relations between international trade law and international environmental norms are construed as a matter of law, for example through in-text references to external norms in World Trade Organization (WTO) treaties, and as a matter of social practice, for example when parties make claims about norm relations in the context of WTO litigation, which can catalyse further norm contestation in other ‘fora’. Tracing these legal developments reveals how the international legal landscape can shift due to frictions between bodies of norms. More often than not, such shifts result in subtle adjustments of the relationships between bodies of norms in tension, leaving the substance of overlapping norms unchanged. In some instances, new norms emerge to regulate these interfaces, giving substance to actors’ expectations of how international trade rules should relate to other norms. In this authority game, advantageously negotiating interfaces between bodies of norms becomes increasingly important. The WTO has played this game rather successfully – to the frustration of environmentalists – by establishing strategic linkages on its own terms.