World food crops have been improved progressively since their domestication about 10,000 years ago. Progress was especially rapid after the rediscovery of Mendel’s laws of inheritance, when scientific principles could be applied to crop improvement. Modern varieties of wheat and rice, which ushered the so-called green revolution and led to the doubling of cereal production in a 25-year period, are examples of recent achievements in increasing crop productivity. The present world population of 5.8 billion is likely to reach 7 billion in 2010 and 8 billion in 2025. Per caput food intake will increase due to improved living standards. It is estimated that we will have to produce 50% more food by 2025. Food grain production in Africa will have to increase almost 400%, in Latin America 200%, and in Asia 60%. In the past, food production grew as a result of increased yield potential of new crop varieties, as well as increases in cropped area. In the future, major increases in cropped area are unlikely. In fact, in most Asian countries the cultivated area is declining due to pressures of urbanization and industrialization. Pesticide use is dropping as a result of concerns about their harmful effects on the environment and on human health. Increasingly, the industrial base is competing with agriculture for water and labor. Thus, we will have to produce more food from less land, with less pesticides, less labor, and less water. Increases in crop productivity are therefore essential to feed the world in the next century. One way to increase crop productivity is to develop crop cultivars with higher yield potential. Of the various strategies for increasing the yield potential, two are reviewed in this chapter. Selection for semidwarf stature in the late 1950s for rice (Oryza sativa L.) and wheat (Triticum aestivum L.) is the most striking example of a successful improvement in plant type. Although selections were guided by short stature, resistance to lodging, and efficient biomass partitioning between grain and straw, breeders were unintentionally selecting for improved canopy architecture, light penetration, and other favorable agronomic characteristics (as reviewed by Takeda, 1984).