This chapter examines the essential role of phosphorus (P) in plants and how plants have evolved to maintain the supply of P to these essential functions. The chapter discusses the concept of P-replete plants and what this means regarding both their physiological and genomic state and how this information can be used to manage crops more effectively. The chapter explores the inherent difference in P-replete status and response to P deficiency seen between crop species and genotypes of crop species, and discusses trade-offs between responses within an individual. The chapter concludes with discussion of what a crop ideotype for efficient use of P might be like and looks ahead to how this information might impact our ability to design and implement sustainable agricultural systems in the future. Finally, the chapter provides detailed suggestions for further reading.