We assess Penrose’s Theory of the Growth of the Firm (1959) based on aggregate findings to date and suggest that her theory may be useful to unify the fragmented field of growth research. We develop theoretical constructs originating in Penrose’s theory and analyze the overall and relative strength of their relationship to firm growth by using meta-analysis techniques on 128 samples, 531 bivariate correlations and a total sample size of 57,659 firms. Our results support many of Penrose’s arguments, identify gaps where further research is needed and provide concrete empirical recommendations for future research on firm growth. We discuss implications for future research which will allow consistent knowledge accumulation and stimulate stalled theoretical development on firm growth.