IESBA: New guidance re External Experts and Sustainability Assurance

IESBA: New guidance re External Experts and Sustainability Assurance

• 17 September 2025
• Audit
• South African Accounting Academy

Summary:
The International Ethics Standards Board for Accountants (IESBA) has released 2 new staff publications to enhance understanding and support global adoption and implementation of its ethics standard on Using the Work of an External Expert as well as the International Ethics Standards for Sustainability Assurance (including International Independence Standards) (IESSA), both of which are effective from December 2026.
Article:
These publications explain key aspects of the standard related to using the work of an external expert and the proportionality of the ethics and independence provisions for sustainability assurance in the International Ethics Standards for Sustainability Assurance (including International Independence Standards) (IESSA).

1. Questions and Answers on Using the Work of an External Expert 

https://www.ethicsboard.org/publications/iesba-staff-questions-answers-using-work-external-expert-0 

This 16-page publication is relevant to all professional accountants, whether in business or in public practice, and sustainability assurance practitioners (SAPs). It provides answers to common questions on:

• Evaluating whether to use the work of an external expert 
• How to identify an external expert
• The extended requirements for evaluating the objectivity of an external expert in the context of an audit or other assurance (including sustainability) engagement
• Concluding an external expert’s competence, capabilities and objectivity
• Potential threats arising from using the work of an external expert
• Specific considerations related to the IESSA 

Access other resources relating to this standard on the IESBA Experts Page at https://www.ethicsboard.org/publications/final-pronouncement-using-work-external-expert 

2. Proportionality of the IESSA https://www.ethicsboard.org/publications/iesba-staff-publication-proportionality-iessa 

This 10-page publication highlights key aspects of the IESSA that illustrate its proportionality, while the IESSA also provides a robust global ethics and independence baseline for sustainability assurance engagements (SAEs). The proportionality of the IESSA enables it to support the performance of SAEs for entities of all sizes, thereby underpinning public trust in those engagements.

The publication is especially geared towards facilitating the implementation of the IESSA by SAPs that are small and medium practices (SMPs).

Access other resources relating to the IESSA on the IESBA Sustainability Page at https://www.ethicsboard.org/focus-areas/global-ethics-sustainability-standards  

Click here to download the documents:

• https://ifacweb.blob.core.windows.net/publicfiles/2025-09/IESBA%20Staff%20Q%26A%20Using%20the%20Work%20of%20an%20External%20Expert.pdf 
• https://ifacweb.blob.core.windows.net/publicfiles/2025-09/IESBA%20Staff%20Publication%20-%20Proportionality%20of%20IESSA.pdf

Relevance to Auditors, Independent Reviewers & Accountants:

• As an accountant, auditor and independent reviewer, you need to be aware of and consider the information contained in publications by various professional bodies and standard-setters, e.g. IESBA, IAASB, etc. – so that you can apply this in the performance of your duties – especially with regards to sustainability assurance and the related ethics.
• IESSA must be applied by all sustainability assurance practitioners (SAPs), and should also be used by professional accountants (PAs) involved in sustainability reporting.

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