Although flows into ESG funds have risen dramatically, it remains unclear whether these funds are truly committed to sustainable investments and how much their investments matter. We shed light on this debate by examining the incentives of fund managers. We find that conditional on similarly large ESG investments, ESG funds vary in their incentives to engage with portfolio firms. ESG funds with higher incentives to engage – committed ESG funds – hold their ESG investments longer, pay more attention to firms’ ESG risk exposure and implement less negative screening. Strikingly, only investments by committed ESG funds contribute to real ESG-improvements, and these funds have outperformed other ESG funds on their ESG holdings. Our paper highlights the importance of incentives when assessing the real impacts of sustainable investments and calls for greater investor awareness of a hidden form of greenwashing.