Technical Abstract: The rising concentration of carbon dioxide in the atmosphere represents an increase in a growth-limiting resource for many crop species. Identification of lines or characteristics of lines which have superior yield at elevated carbon dioxide could aid in adaptation to this global change. While intraspecific variation in responses to elevated carbon dioxide has been found in several species, intraspecific differences in crop yield responses to elevated carbon dioxide under field conditions have seldom been documented. In this four-year study, the responses of photosynthesis, growth, pod number, seed number and size, and seed yield to ambient and 1.5 times the ambient concentration were examined in four varieties of common bean in the field, using open-top chambers. There was a significant variety by carbon dioxide concentration interaction for seed yield, with seed yield at elevated carbon dioxide ranging from 0.89 to 1.39 times that at ambient carbon dioxide in the different varieties, when averaged over four years. The highest yielding variety at elevated carbon dioxide was not the highest yielding variety at ambient carbon dioxide. The varieties with the largest and smallest yield responses both had an indeterminate growth habit. Down-regulation of photosynthesis at elevated carbon dioxide only occurred in the two indeterminate varieties, and there was no significant correlation between the response of single leaf photosynthetic rate and the response of seed yield to elevated carbon dioxide among varieties, nor between the responses of stem mass and seed yield. The change in the number of pods at elevated carbon dioxide was the primary determinant of the response of seed yield.