Firms seek independent assurance from accountants on their Corporate Social Responsibility (CSR) disclosures for various reasons, including to enhance the credibility of such disclosures or to enhance the reliability of management's CSR report. However, there are multiple levels of assurance available for CSR disclosures. The forthcoming clarified U.S. attestation standards re-frame the two levels of assurance on non-financial information as reasonable (higher) and limited (lower). While not currently addressed by U.S. standards, accountants also issue hybrid reports with both reasonable and limited assurance on CSR disclosures. I conduct an experiment to identify differences in nonprofessional investors' perceptions of CSR disclosures when reasonable, limited, or hybrid assurances are provided and manipulate firm CSR performance as a possible moderator for the influence of assurance. Findings indicate that nonprofessional investors find CSR disclosures on greenhouse gas emissions to be credible, and the degree of credibility does not vary significantly based on the firm's performance in controlling emissions or on the level of assurance provided by an accountant. However, nonprofessional investors do differ in their perceptions of the overall reliability of representations made in management's CSR report. While management's CSR report supported by hybrid assurance is generally perceived to be as reliable as when only limited or only reasonable assurance is provided, the perceived reliability differs between limited and reasonable assurance. Supplemental analyses reveal an interaction such that management's CSR report is perceived as more reliable with limited assurance rather than with reasonable or no assurance for firms with better performance at controlling greenhouse gas emissions; this association reverses for firms with worse performance. This interaction may be due, in part, to language in limited assurance reports that makes it clear higher assurance was available but not pursued by management. Results address a gap in the literature for hybrid assurance and show that nonprofessional investors find management's CSR report with hybrid assurance to generally be as credible and reliable as when either limited or reasonable assurance is provided. Further, results offer insight into the interactive effects of firm performance and level of assurance on nonprofessional investors' perceptions of the reliability of management's CSR report. / Ph. D.