Sustainability Assurance under CSRD: Evaluating Audit Firms’ Readiness and Methodological Approaches
Sustainability Assurance under CSRD: Evaluating Audit Firms’ Readiness and Methodological Approaches

Author(s): Nikoleta Stoykova
Subject(s): Politics / Political Sciences, Politics, Economy, Business Economy / Management, EU-Approach / EU-Accession / EU-Development, Accounting - Business Administration
Published by: Университет за национално и световно стопанство (УНСС)
Keywords: CSRD; ESRS; ISSA 5000; sustainability assurance; audit readiness
Summary/Abstract: This paper assesses the preparedness of European audit firms to deliver sustainability assurance in accordance with the Corporate Sustainability Reporting Directive (CSRD) and the initial European Sustainability Reporting Standards (ESRS). The CSRD broadens the requirements for corporate sustainability reporting by mandating a sustainability statement within the management report, which must undergo external assurance. Currently, this assurance is limited in scope, with discussions ongoing regarding a shift to reasonable assurance. The International Auditing and Assurance Standards Board (ISSA 5000) and the Committee of European Auditing Oversight Bodies (CEAOB) have issued guidance to promote consistent practices across European jurisdictions. This study employs a comparative documentary review covering the period 2022 to 2025, drawing on three primary sources: European Union legal and regulatory documents (including the CSRD, ESRS, Commission Frequently Asked Questions, and 2025 Omnibus proposals), professional and supervisory guidance (such as ISSA 5000, CEAOB Guidelines, and Accountancy Europe publications), and market evidence from transparency reports and practitioner literature. The analysis categorizes documents into five areas: regulatory alignments, while smaller firms face significant capacity gaps in data quality, controls, and specialist expertise. The findings indicate alignment among firms regarding risk-based limited-assurance processes, especially in materiality assessment, value-chain evidence collection, and data lineage tracking. Firms are increasingly utilizing structured tools, including scoping matrices, materiality logs, and lineage checklists. Nonetheless, significant differences remain in the implementation of double materiality, the reliability of value-chain estimates, the preparation of forward-looking disclosures such as transition plans and scenario analyses, and the development of internal controls. Large audit networks and jurisdictions with numerous public-interest entities demonstrate greater readiness, whereas smaller firms experience substantial gaps in data quality, internal controls, and specialized expertise. The Bulgarian context offers further perspective. National legislation and official guidance specify the required location of the sustainability statement and delineate responsibilities between management and assurance providers. Transparency reports indicate the existence of effective quality management systems and independence safeguards. However, there is limited availability of sustainability-focused training and practical engagement experience. These challenges reflect broader European Union issues related to inconsistent capacity and knowledge gaps. The study identifies several practical measures to enhance assurance readiness, including the development of audit-ready materiality documentation, establishment of evidence hierarchies for value-chain data, implementation of data lineage controls, targeted competence building for environmental, social, and governance (ESG) specialists, and the articulation of clearer scope narratives. Persistent risks include fragmented data, regulatory uncertainty, and excessive reliance on automation. The analysis is constrained by its dependence on publicly available sources and the absence of access to engagement files. Future research should examine live assurance engagements, monitor developments from 2025 to 2028, and analyse report content to standardize scope narratives and clarify inherent limitations.

• Details
• Contents