Phenotyping serves both research and breeding purposes. For research, precise and often costly procedures are employed to phenotype strategic traits in order to gain a better understanding of how genotypes adapt to different environments. For breeding, both strategic and screening traits are considered, the latter typically being measured at high throughput. This chapter describes phenotyping for key traits and environments, as well as the challenges facing reliable phenotyping. The chapter explains applications of phenotyping in breeding, offering a detailed case study of physiological breeding for yield potential and climate change. Finally, the chapter looks ahead to future research trends and suggests further reading in this area.