Existing governance theories offer contrasting views on the potential effect that controlling owners have on a firm's innovation investment decisions: the stewardship perspective suggests a positive influence, whereas the principal-principal (PP) conflict perspective posits a negative influence. In this study, we attempt to reconcile these views. We propose that business group affiliation determines the extent to which the interests of controlling owners and affiliated firms are congruent, and may motivate controlling owners to behave opportunistically. Our analysis of Korean companies shows that controlling owners of independent firms significantly promote R&D investments, particularly when growth opportunities are plentiful. However, the relationship becomes much weaker for business group affiliates.