We find that firms with more gender-diverse boards achieve greater innovative success. The results are not driven by endogenous matching between female directors and firms with high innovative potential. To explore the mechanism, we find that the positive effect of gender diversity on innovation is stronger when product market competition is lower and when managers are more entrenched, consistent with increased oversight by female directors improving manager’s incentives to innovate. Furthermore, we observe that although gender diversity does not enhance firm value on average, it is particularly valuable for firms in which innovation and creativity play an important role.