As an essential input to crop growth via soil reserves or fertilizer, phosphorus underpins global food security. Without phosphorus, food could not be produced, yet phosphorus is mined from fi nite reserves, most of which are controlled by only a few countries1 (UNEP 2011; Jasinski 2015; Cordell and White 2014). Fertilizer prices are likely to increase as fi nite reserves become critically scarce. Globally, a billion farmers and their families cannot access fertilizer markets and many rely on phosphorus-defi cient soils that produce low crop yields (IFPRI 2003). Moreover, mismanagement along the phosphorus supply chain from mine to fi eld to fork has resulted in massive losses and waste, which largely ends up in waterways, causing nutrient pollution and algal blooms (Bennett, Carpenter and Caraco 2001). The global phosphorus challenge is inherently complex; it is as much about international relations as farm soil fertility. It transcends disciplines, sectors, and scales – from geopolitics to ecology to nutrition. In this chapter, we describe and refl ect upon a new project using a novel transdisciplinary approach to address this phosphorus challenge.