Sustainability reporting received considerable attention worldwide since the beginning of this millennium. This attention and increasing trend towards sustainability reporting is clear since the issuance of the UN Agenda 2023 in 2015. Since then, countries and firms are placing more emphasis on their nonfinancial performance and activities and are encouraged to report theses activities, consistent with the stakeholders theory, to receive support from different stakeholders that influence the firms' success. Without any doubt, the increasing sustainability reporting and disclosures will create a demand on assurance services, which in turn may be provided by the firms' external auditors. This assurance will add value to the sustainability reports issued by firms through increasing users confidence in the credibility of the related sustainability information.
The objective of this paper is to shed the light on sustainability reporting, assurance on this nonfinancial reporting in accordance with the International Standard on Assurance Engagements 3000 (ISAE 3000), and the effect of this assurance on stakeholders' reliability on the information content of such reports. This paper adds to the extant sustainability reporting and assurance literature and will provide valuable insights to auditors, company managers, standards setters, policymakers, market participants and the business community in general.