This chapter analyzes the interactions between a for-profit private actor, the pharmaceutical company Merck, and a public international institution, the World Health Organization, in order to fight river blindness (onchocerciasis), a neglected tropical disease. The chapter shows how, starting from the 1970s, cooperation between the two contributed not only to the creation of a drug donation program (the Mectizan Donation Program) but also to the forging of a new model for international health policies on neglected diseases. It adopts a socio-historical approach to develop the ‘thick description’ of a single case study and the tracking of institutional processes and social interactions. The chapter demonstrates how both actors shape each other, how their increased interdependence transforms and co-constitutes the field of the fight against onchocerciasis, both in terms of policy content (a donated drug taken by humans replaces vector control programs) and in terms of institutional shape (creation of new structures and involvement of new actors in the fight against the disease – experts, communities, and NGOs). It also illuminates larger trends in the co-constitution of international policies, as this case prefigures contemporary debates on the increased participation of non-state actors (NGOs, philanthropic foundations, corporations, etc.) in the design of global public policies.