Agro-food systems are fuelled by nitrogen. About 80% of this valuable resource is lost to the environment before reaching our plates. We refer to this loss as nitrogen waste. The ambitious goal of halving nitrogen waste by 2030 requires important coordination of many actors: multidisciplinary scientists, farmers, industry, policy-makers, NGOs, and consumers. The XXI International N Workshop will contribute to this challenge by welcoming contributions dealing with different spatial scales (from the plot to global) and system scopes (crop, livestock,…