We provide the first large-sample evidence on third-party verification of firms’ environmental and social metrics in ESG reports (ESG assurance) in the United States. Focusing on the S&P 500 from 2010–2020, we document a striking increase in not only the number of firms with ESG assurance—in 2020 (2010), 76% (38%) of the S&P 500 had an ESG report and 46% (16%) involved assurance—but also the number of metrics assured. Unlike financial audits, ESG assurance varies widely in form and substance, including the choice of metrics assured, the level of assurance, and assuror identity. We show that firms’ decision to obtain ESG assurance is primarily driven by their adoption of ESG reporting frameworks and peer effects, with firm characteristics documented in prior literature playing only a minor role. Assurance is associated with improvements in ESG disclosure, ESG ratings, and the number of institutional investors holding the firm’s stock

Using a novel measure that captures negative ESG incidents at both listed and private suppliers, we provide large-scale evidence on the value implications of supply chain ESG. We find that firms with fewer supply chain ESG incidents exhibit higher future accounting performance and that this effect is stronger in the presence of more conscious customers and vulnerable supply chains. We also find that firms with robust supply chain ESG exhibit higher future stock returns and that this effect is more pronounced when information frictions are higher, which suggests that it takes time for the market to understand the value implications of supply chain ESG. Overall, we highlight the benefits of managing supply chain ESG and the decision usefulness of the related information

The Sustainability Accounting Standards Board (SASB) has classified sustainability topics as material or not material for investors. We leverage the staggered release of the SASB classifications from 2013 to 2016 to examine whether and how they prompt changes in U.S. firms' sustainability performance. We measure sustainability performance using RepRisk scores, which reflect environmental, social, and governance (ESG) incidents. We find that RepRisk scores on sustainability topics classified as material decrease following the release of SASB classifications. Conversely, incident scores on nonmaterial sustainability topics increase. This suggests that firms improve their sustainability performance on topics the SASB deems relevant for investors while simultaneously performing worse on irrelevant topics. Firms adjust their internal sustainability policies to mirror these changes. The changes in sustainability performance occur primarily through two channels. We document that higher exposure to the classifications from shareholder pressure and sustainability-linked executive compensation prompts managers to prioritize sustainability topics classified as relevant for investors over irrelevant ones