This chapter describes advances in understanding and improving the use of macro-minerals in poultry with a particular focus on phosphorus (P). The chapter begins by outlining the challenges to optimising mineral nutrition in poultry, covering the characterisation of the P value in feed ingredients and factors that affect P availability. Next a section on case studies is explored, including a meta-analysis for assessing the P value of a diet and a model where the P and calcium (Ca) quantities required for maintenance and growth are aggregated to determine the overall needs of the animals. Finally, future trends are discussed, covering precision feeding for sustainability, the potential for compensatory mechanisms and genetic determinism, the balance between Ca and P in laying hens, and a digestible Ca system.