In the past 20 years large advances have been made in the physiological understanding of most processes that influence soybean development, growth, and yield. Certainly the accumulating knowledge base in soybean is substantial for photosynthesis, N₂ fixation, plant ontogeny, seed growth, and drought stress. While little change in physiological performance between modem cultivars and older lines have been found for a number of traits, manipulation of plant ontogeny has been critical in the adaptation of cultivars to specific environmental zones. Future improvements seem possible in a number of physiological traits. Ontogenetic adaptations are likely to be improved, especially in the tropics, as the long-juvenile gene is exploited. Improvements in seed traits, particularly seed quality, are being incorporated into new germplasm. Increased rates of nitrogen fixation and amelioration of soybean sensitivity to drought stress are anticipated physiological advances.