This paper brings a constitutional economics perspective to bear on the World Health Organization (WHO), the flagship United Nations intergovernmental health organisation, which is obligated by its Constitution to achieve 'the highest possible level of health' for the world's peoples. The WHO has in the seven decades of its existence used its formidable legislative powers only sparingly. It has been widely chided for being weak in regional coordination and unresponsive to transnational emergencies like the West African Ebola outbreak of 2014-2016. In 2020, it found itself at the centre of the COVID-19 pandemic and in the middle of the Sino-American geopolitical tug-of-war. This paper traces the discordance between the Constitution's stated purposes and the actual track record of the WHO not back to its organisational culture nor to weak leadership but to the design of the Constitution itself. It analytically distinguishes the Constitution's expressive from its instrumental halves, and shows that, whilst the former embodies a 'constitutional moment' of international health solidarity right after the Second World War, the latter embodies a reserved and limited delegation from member-states that are jealous of their sovereignty.