Public policy makers seek to enhance disclosure of firms’ sustainability performance, yet firms debate about whether, or to what extent, they should engage in sustainability reporting. This article seeks to advance current understanding about the business returns to sustainability reporting by examining the short- and long-term investor reactions. Through an event study, this research documents significant short-term stock market reaction to the release of sustainability reports. In particular, abnormal stock returns around the release of such reports are positively related to firm sustainability performance, and this positive link is smaller for firms in a strong information environment. The results show that over the long term, relative to nonreporting firms, firms that release sustainability reports enjoy higher value relevance of sustainability performance. These findings suggest that sustainability reports enhance information transparency and allow investors to incorporate sustainability information in stock valuation. This study provides strong evidence for the business case of sustainability reporting, and offers important implications for public policy makers in terms of devising policies and regulations to promote sustainability reporting.