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 finite reserves, most of which are controlled by only a few countries. Fertilizer prices are likely to increase as finite reserves become critically scarce. Globally, a billion farmers and their families cannot access fertilizer markets and many rely on phosphorus-deficient soils that produce low crop yields. Moreover, mismanagement along the phosphorus supply chain from mine to field to fork has resulted in massive losses and waste, which largely ends up in waterways, causing nutrient pollution and algal blooms. 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 reflect upon a new project using a novel transdisciplinary approach to address this phosphorus challenge.