Debates about ‘constitutionalism’ have become an important trend in WTO scholarship. Despite over two decades of interest, however, a coherent definition of the term and its content remain out of reach. This paper argues that ‘constitutionalism’ should be approached not as something that can be measured or assessed empirically, but rather as a ‘discursive contest’: a debate in which participants intervene on behalf of particular understandings of how the system does or should operate. Approaching constitutionalism as a discursive contest adds to the literature by shifting the focus to an analysis of how ‘constitutional talk’ produces knowledge about the WTO, and how this knowledge in turn structures perceptions about the way government works and the possibilities for action. Providing examples from scholarly debates and WTO practice, the article aims to make concrete the relationship between truth and government and the implications of discursive contests over constitutionalism in the field of WTO law.