Carl W. Weuster, Philipp Ottenstein, Sébastien Jost, Sophie Winter

• The spread of CSR reporting is accompanied by an increase of external assurance. Firms are employing assurance to signal the credibility of their CSR reports towards stakeholders and improve their reputation. Whether this practice is socially and economically beneficial remains up for debate. The research question of this paper concerns whether external assurance is associated with transparency in CSR reports. A panel data model is used to iestigate the empirical relationship of external assurance and three indicators of transparency: reporting scope as an indicator for completeness, readability as an indicator for clarity and optimism as an indicator for reporting balance, with the latter two proxies derived from text analysis.We find an ambiguous relationship between external assurance and reporting transparency: External assurance is positively related to reporting scope and negatively to optimism and readability. This study adds to the scarce literature on external assurance for CSR reporting. We contribute one of the first iestigations on how external assurance relates to linguistic aspects of CSR reporting transparency. Keywords CSR reporting, external assurance, Europe, readability, optimism, computer-aided text analysis