When delegates, panellists and speakers arrived at Chartered Accountants’ Hall on 3 March 2025 for our event on ‘New International Standards for Sustainability Assurance’, they were not short of things to talk about. Years of research and development have recently led to some big advances towards global baseline standards for sustainability reporting and assurance, as policymakers, regulators, standard-setters and a broad range of market participants together created the foundations of a new external reporting ecosystem.

New era of external reporting

“Events such as this are essential to build knowledge, to exchange ideas and experience, and to guide standard-setters, regulators and practitioners as we embark on this sustainability journey together,” said Tom Seidenstein, Chair of the International Auditing and Assurance Standards Board (IAASB), during his keynote address. Stakeholders increasingly expect a broad range of non-financial and financial information to help them understand and assess corporate performance and for this to include sustainability-related information. 

These expectations are reflected in the recent arrival of European Standards for Sustainability Reporting (ESRS) and global IFRS Sustainability Disclosure Standards (IFRS S1 and S2). As a credible and trusted reporting ecosystem also needs expert, ethical and independent third-party assurance, these (and other) new reporting standards have been joined by new global standards for assurance, from both the IAASB and the International Ethics Standards Board for Accountants (IESBA) to create a complete package for global sustainability disclosure.

‘Building trust with sustainability assurance’ was the subject of presentations at our event by Josephine Jackson, Vice-Chair of the IAASB and ISSA 5000 Technical Implementation Contact Group Chair, and by Mark Babington, an IESBA Member and Sustainability Task Force Chair. They introduced:

• the IAASB’s recently published International Standard on Sustainability Assurance (ISSA) 5000, General Requirements for Sustainability Assurance Engagements and Conforming and Consequential Amendments to Other IAASB Standards Arising from ISSA 5000; and
• IESBA’s International Ethics Standards for Sustainability Assurance (including International Independence Standards) (IESSA), which is a new Part 5 of the IESBA Code of Ethics for Professional Accountants, and revisions to the IESBA Code to add material on Using the Work of an External Expert.

Both standard-setting bodies have created factsheets, Q&As, videos, webinars and other support resources to assist providers and users of sustainability reports and assurance (see links below) and more are planned for 2025 and beyond. 

In jurisdictions adopting the standards, both ISSA 5000 and the IESSAs are effective from 15 December 2026 with early adoption permitted and encouraged.

Working together

The IAASB and IESBA have worked closely during development of these new sustainability assurance standards. Both standard-setting bodies have built on well-established and familiar foundations, harmonising concepts and using common terminology and definitions, to craft a well-coordinated and aligned package of requirements. 

Babington and Jackson both considered how these new standards will impact various stakeholder groups, including reporting companies, assurance providers and those who rely on their sustainability-related reports. Some of the more challenging aspects were acknowledged during these presentations. They were also talking points during the subsequent panel session, when Babington and Jackson were joined by Seidenstein, plus practitioner members of the Technical and Practical Auditing Committee of the Audit and Assurance Faculty.

Panel moderator Paul Winrow, Partner of Public Policy and Regulation at Forvis Mazars, and Matthew Stroh, who leads Grant Thornton UK’s Audit Technical Team, brought to the discussion their experiences of preparing to implement the new sustainability assurance standards and some thorny considerations for assurance providers. Flexibility, proportionality and scalability featured; likewise issues around connectivity between financial statements and sustainability disclosures and reporting, estimates and forward-looking information, using the work of other experts, and information on sustainability value chain components.

All of this and more will be considered further in Audit & Beyond going forward, offering expert insights and practical pointers on challenges and ways to address them, from our presenters and panellists.

Meanwhile, assurance providers can stay on top of existing and emerging developments by exploring the wealth of resources made available by the IAASB and IESBA to support implementation.