This chapter shows that quantitative integration of crop growth and development with mathematical models can provide new insights to ideotypes through "optimization" of crop structure and behavior. Variation and uncertainty are major constraints to optimality. Sources of variation and uncertainty come from weather, spatial differences (soil and topography) within and between fields, price, knowledge and skill of managers and operators, and quality and settings of machinery, as well as normal biological variation. Although large voids remain in one's understanding of temperature relations, growth, and development, improved understanding will probably provide only marginal gains. Marginal gains are the essence of both agriculture and optimization. Because future gains in yield are likely to be marginal and to come counterintuitively from subtle traits, optimization methods may prove extremely helpful. Whether such approaches will prove superior to traditional empirical methods remains to be seen.