On 14 August 2025, IAASB published materials to clarify ISSA 5000’s interaction with ISAE 3000 and ISAE 3410, and to show separately what ISSA 5000 looks like for reasonable and limited assurance.

IAASB has followed up its November 2024 ISSA 5000 standard, and related January 2025 implementation guidance, with a further string of guidance documents to help practitioners with implementation.

Interaction with ISAE 3000 (Revised) and ISAE 3410

Firstly, an FAQs document to clarify how ISSA 5000 interacts with extant assurance standards – or where those standards will no longer apply.

A reminder that ISSA 5000 is effective for assurance engagements on sustainability information reported for periods beginning on or after 15 December 2026 or as at a specific date on or after 15 December 2026.

The FAQs state that for ISAE 3000 (Revised):

• ISAE 3000 (Revised) generally cannot be used for sustainability assurance engagements after ISSA 5000 becomes effective; 
• except where a jurisdiction hasn't adopted ISSA 5000 (or hasn't adopted it yet) but where ISAE 3000 (Revised) is in place, in which case it can continue to be used.

And for ISAE 3410 on greenhouse gases:

• ISAE 3410 generally cannot be used once ISSA 5000 becomes effective. 
• But again, there is a situation in which it might be, and that is if law or regulation in that jurisdiction requires the use of a jurisdiction-specific version of ISAE 3410 after the effective date of ISSA 5000. 
• However, practitioners in that jurisdiction will not be able to claim compliance with IAASB standards for assurance engagements on sustainability information unless they apply ISSA 5000 for those engagements from its effective date.

“Extracts for limited assurance and reasonable assurance engagements”

Alongside the FAQs on ISAE 3000 (Revised) and ISAE 3410, the IAASB also published two “staff extracts” for limited assurance and reasonable assurance engagements. 

These extracts the sections within ISSA 5000 that are relevant to limited and reasonable assurance engagements, so that they can be read separately, following demand from stakeholders.

The IAASB makes it clear that they are simply for reference purposes and practitioners should still read ISSA 5000 in full. Consequently, while ISSA 5000 is authoritative, these extracts “do not constitute an authoritative or official IAASB pronouncement”.

• Extract of limited assurance material
• Extract of reasonable assurance material

ICAEW’s Audit and Assurance Faculty has published a range of guidance on sustainability assurance, and is actively involved in responding to UK government and FRC consultations on sustainability assurance.

• ICAEW Sustainability Assurance hub
• ICAEW Climate Assurance hub (for directors and audit committee members)
• Response to the FRC on ISSA (UK) 5000

The following articles on assurance can be accessed by Audit and Assurance Faculty, ICAEW members and ACA students.

• Engaging with sustainability assurance
• The sustainability assurance and reporting landscape
• Is your sustainability assurance house in order?

You can also learn all about sustainability through ICAEW's e-learning programme, Sustainability Accelerator, which is freely available for ICAEW members.