Yield potential is a commonly used term but its definition and measurement are quite vague. The absence of agreement in its definition and measurement can lead to misunderstanding and to misleading claims. Considering concepts in literature, this paper has adopted a clear definition and distinction between yield potential and potential yield. Yield potential is the yield of a cultivar when grown in environments to which it is adapted; with nutrients and water nonlimiting and with pests, diseases, weeds, lodging, and other stresses effectively controlled. Potential yield is the maximum yield that could be reached by a crop in given environments such as those determined by simulation models with reasonable physiological and agronomic assumptions. Direct and indirect measurements of progress in yield potential among crops have been discussed in this paper with care for complications arising from cultivar by environment interaction.