International trade is undergoing a transformation commonly referred to as 'constitutionalization'. Despite the ubiquity of the phrase, its meaning remains ambiguous and its significance underexplored. The purpose of this article is to suggest that one plausible interpretation of 'constitutionalization' in the international trade law context is that it refers to the generation of a set of constitutional-type norms and structures by judicial decision-making in the Appellate Body of the World Trade Organization. Unlike the work of John Jackson, Ernst-Ulrich Petersmann and Joseph Weiler (emphasizing institutions, rights and metaphysics respectively), this article will focus on judicial constitutionalization. Four trends will illustrate this: constitutional doctrine amalgamation, system constitution, subject matter incorporation, and constitutional value association. The identification of these trends reveals the underlying structure of the constitutionalization debate. Visible through the tribunal's carefully crafted formulations of rules and justifications are the mainstay principles of constitutional reasoning (democracy and governance, constitutional design, fairness, and allocation of policy responsibility). Ultimately the arguments presented here convert the discussion from a debate about whether the WTO is a constitution into a set of speculations on the nature of international trade, and on the valency of the idea of constitutionalization.