In this chapter, the authors analyze the changes produced by breeders in wheat yield during just the last century, when scientific genetic improvement took place after the rediscovery of Mendel's laws. The main objectives in writing the chapter were to identify the contributions of breeding to the improvement in wheat grain yield and the major physiological attributes that were modified with grain yield and grain protein as a result of the genetic improvement of wheat grain yield potential. In this chapter, the authors have outlined most of these changes with the objective of summarizing those traits that could be useful in future breeding. Austin et al. and Slafer et al. showed that genetic improvement in wheat grain yield has led to decreases in grain protein percentage. Future breeding should exploit the genetic variability in physiological attributes to increase total biomass of the crop, maintaining present levels of partitioning between vegetative and reproductive tissues.