Performance differences between firms are generally attributed to organizational factors rather than to differences among the individuals who make up firms. As a result, little is known about the part that individual firm members play in explaining the variance in performance among firms. This paper employs a multiple membership cross-classified multilevel model to test the degree to which organizational or individual factors explain firm performance. The analysis also examines whether individual differences among middle managers or innovators best explain firm performance variation. The results indicate that variation among individuals matter far more in organizational performance than is generally assumed. Further, variation among middle managers has a particularly large impact on firm performance, much larger than that of those individuals who are assigned innovative roles. Copyright © 2012 John Wiley & Sons, Ltd.